We had a situation where we have to find out all the details of a product with the Nth highest price Note: Some of the products are in the same price range.

Here I am demonstrating with employee table. Create the table “Employee” from the below script.

USE [udayarumilli];
GO
CREATE TABLE [dbo].[Employee](
    [empid]     [int] IDENTITY(1,1) NOT NULL,
    [name]      [nvarchar](20) NOT NULL,
    [birthdate] [datetime] NOT NULL,
    [Salary]    [int] NOT NULL
) ON [PRIMARY];
GO
INSERT INTO [Employee] ( name,birthdate,Salary)
VALUES ('Sara Davis',1958-12-08,120000),
('Don Funk',1962-02-19,98000),
('Judy Lew',1973-08-30,76000),
('Yael Peled',1947-09-19,76000),
('Sven Buck',1965-03-04,102000),
('Paul Suurs',1973-07-02,110000),
('Russell King',1970-05-29,69000),
('Maria Cameron',1968-01-09,72000),
('Zoya Dolgopyatova',1976-01-27,89000)
GO

Now let’s check the employee salaries using the below query.

SELECT      Salary
FROM         Employee
ORDER BY  salary DESC;
GO

From the table we can say that highest salary is: 120000 and lowest salary is: 69000

Now we‘ll see the different options how can get the employee details for Nth highest salary.

There are mainly two ways we can accomplish this as below. We’ll find the 3rd highest salary.

-- Traditional way to find the 3rd highest salaried employee details

SELECT TOP 1 name,salary
FROM (
        SELECT DISTINCT TOP 3 name,salary
        FROM        employee
        ORDER BY    salary DESC) e
ORDER BY salary
 

-- Using ROW_NUMBER() to find the 3rd highest salaried employee details

SELECT    name,salary
FROM(
        SELECT name,Salary,
               row_number() over(order by salary desc) as place
        FROM   employee) e
WHERE e.place=3

From the data yes we can confirm these are giving the 3rd highest salaried employee details.

 From the above queries if you want to find the 4th highest just replace 3 with 4 and if Nth highest required replace 3 with N.

 Now we’ll try to find out the 6th highest salary using the same queries.

 -- Traditional way to find the 6th highest salaried employee details

SELECT TOP 1 name,salary
FROM (
        SELECT DISTINCT TOP 6 name,salary
        FROM        employee
        ORDER BY    salary DESC) e
ORDER BY salary

-- Using ROW_NUMBER() to find the 6th highest salaried employee details
SELECT    name,salary
FROM(
        SELECT    name,Salary,row_number() over(order by salary desc) as place
        FROM    employee) e
WHERE e.place=6

Here is the problem. If you can observe there are two employees with the same salary

But these queries are retrieving only one record that is 6th row: Judy Lew. But there are two employees with the same salary which is 6th highest in the group.

If we try to capture the 7th highest it gives us the wrong result. It might be 6th row or 7th row depends on the ORDER BY clause.  To avoid this we have to change the query to use DENSE_RANK() instead of ROW_NUMBER().

-- Using DENSE_RANK() to find the 6th highest salaried employee details

SELECT  name,salary as '6th_Highest'
FROM(
        SELECT  name,Salary,
                DENSE_RANK() over(order by salary desc) as place
        FROM    employee) e
WHERE e.place=6

-- Using DENSE_RANK() to find the 3rd highest salaried employee details
SELECT    name,salary AS '3rd_Highest'
FROM(
        SELECT  name,Salary,
                DENSE_RANK() over(order by salary desc) as place
        FROM    employee) e
WHERE e.place=3

Now we can see all the employees who are at the 6th highest salary are included in the result set.

Both NEWID() and NEWSEQUENTIALID() are used to generate GUID of data type UNIQUEIDENTIFIER in SQL Server.

The Basic difference between them is NEWID() generates GUID’s in random order whereas NEWSEQUENTIALID()  generates GUID’s in a sequential order.

We can generate a GUID just by calling NEWID() but we can’t directly use NEWSEQUENTIALID() for generating GUID’s from select statement.

Since NEWID() generates random GUID’s it leads to have more page splits in indexes compare to NEWSEQUENTIALID().

Examples:

1. Now let’s see how both of them generates GUID’s    

To understand them properly lets create a table insert data and create cluster indexes.

/****** Drop the table if exists ******/
IF EXISTS (SELECT 1 FROM sysobjects WHERE TYPE = 'U' and NAME = 'Product_NewID')
BEGIN
    DROP TABLE Product_NewID;
END
GO
/****Create table with NEWID() ***/
CREATE TABLE Product_NewID(
    ProductID    UNIQUEIDENTIFIER DEFAULT(NEWID()),
    ProductName    VARCHAR(100) NOT NULL,
    ProductPrice    DECIMAL(10,3) NOT NULL DEFAULT(0.000),
    UpdatedDate    DATETIME NOT NULL DEFAULT(SYSDATETIME())
);
GO
IF EXISTS (SELECT 1 FROM sysobjects WHERE TYPE = 'U' and NAME = 'Product_NewSEQID')
BEGIN
    DROP TABLE Product_NewSEQID;
END
GO

/****Create table with NEWSEQUENTIALID() ***/
CREATE TABLE Product_NewSEQID(
    ProductID    UNIQUEIDENTIFIER DEFAULT(NEWSEQUENTIALID()),
    ProductName    VARCHAR(100) NOT NULL,
    ProductPrice    DECIMAL(10,3) NOT NULL DEFAULT(0.000),
    UpdatedDate    DATETIME NOT NULL DEFAULT(SYSDATETIME())
);
GO

/**** Create clustered indexes as below ****/
CREATE CLUSTERED INDEX ix_Product_NewID_ID ON Product_NewID(ProductID);
GO
CREATE CLUSTERED INDEX Product_NewSEQID_ID ON Product_NewSEQID(ProductID);
GO

/*** Now insert data into these two tables ****/
INSERT INTO Product_NewID (ProductName,ProductPrice)
VALUES ('Product_11109',233.56);
GO 20000

INSERT INTO Product_NewSEQID (ProductName,ProductPrice)
VALUES ('Product_11109',233.56);
GO 20000

Now we’ll see just by selecting data from them

You can see all “ProductID” column values are randomly generated.

Now we’ll look into the other table where we have used NEWSEQUENTIALID().

From the above picture we can see the “ProductID” values are sequentially generated.

2. Now we‘ll see how these differentiate with the select statement.

SELECT NEWID();
GO
SELECT NEWSEQUENTIALID();
GO

NEWID() is generating a GUID. We’ll try with NEWSEQUENTIALID()

It results into an error message:

Msg 302, Level 16, State 0, Line 1

The newsequentialid() built-in function can only be used in a DEFAULT expression for a column of type ‘uniqueidentifier’ in a CREATE TABLE or ALTER TABLE statement. It cannot be combined with other operators to form a complex scalar expression.

3. Difference between NEWID() and NEWSEQUENTIALID() in page allocation

 We have already inserted 20000 rows into two tables.

Product_NewID: Used NEWID()

Product_NewSEQID: Used NEWSEQUENTIALID()

DBCC SHOWCONTIG('Product_NewID');

DBCC SHOWCONTIG('Product_NewSEQID');

For the same 20000 rows inserted in these tables we can check observe how pages are allocated for each of these tables.

For the table Product_NewID

Pages Scanned: 218

Avg. Bytes free per page: 2499.7

For the table Product_NewSEQID

Pages Scanned: 152

Avg. Bytes free per page: 69.2

From the above values we can say that there is higher fragmentation for the table which is using NEWID() when comparing with the table which is using NEWSEQUENTIALID().

Generating script for Stored procedures and views in SQL Server 2012

Today I have got a question from one of the beginner DBA. He was actually asked to get “CREATE SCRIPT” for 35 stored procedures and 15 views from one of the database.  He started trying to get script for each object one by one and as he doesn’t have clue how to get the task done in a single go.

It may sounds silly for the experienced people but I believe this blog can help the beginners. Now let’s see how to get the script for selected objects from a database.

To demonstrate this I have created few dummy stored procedures and views.

Now let’s see how to take the “CREATE SCRIPT” for all selected objects.

1. Right click on Database name (My database name is “udayarumilli”) , click on “Tasks” and click on “Generate Scripts”

2. A new window opens with the introduction page just click on Next button.

3. There are two options available,

“Script entire database and all database objects” and

“Select specific database object”.

As we are looking to script the specific objects select the second option and then select the list objects those needs to be script out. To do that expand the object type node and select the required objects. For example to select the “Test_v_1” expand the object type “Views” and select the required view “Test_v_1”.

4. Once you selected required objects click on next button. It takes you to the next section “Scripting Options”.

There are different save options available I usually choose “Save to New Query Window”. Apart from this we have two more save options “Save to File” and “Save to Clipboard” we can choose either of these depends on the requirement.

5. Now on the same page click on “Advanced” button to change the scripting configurations.

Once you click on “Advanced” button there will be a new window opens and there you find two group of options “General” and “Table/View Options”. In all of them we usually concentrate on below options.

“Script DROP and CREATE” : There are three options available depends on requirement we can choose one option whether script required for dropping objects, creating objects or drop and creating the object.

“Script for Server Version”: Depends on which server we are going to run this script we can choose the server version from SQL Server 2000 to 2012”.

“Script USE Database”:  Depends on whether we require this statement at the top of the script or not we can choose “True” or “False”. Usually the database names similar at source and destination so we choose “True”.

6. Click on “OK” and then “Next” button. It takes you to the “Summary” phase. Cross check the objects selected and configure options and click on “Next” button.

7. You can check the script at new query window that was generated by “Script Generator”.

8. You can check the report on object wise. This report is really useful when we do script for bulk number of objects.

9. Save the report to your local and open it in internet explorer as below.

10. Go to the query window; once you check the script execute it at the destination machine or save it to a file.

11. Click on “Finish” button to close the window.

SP_SPACEUSED: is a system stored procedure and used to capture number of rows, total size, data and index size information. Sometimes SP_SPACEUSED may give incorrect information. Below are some of the reasons those may leads to give the wrong page / row counts in SP_SPACEUSED. This may because of below reasons.

1. Statistics are not updated for a long time

2. Index maintenance is not being organized

3. Huge number of DDL operations

If you find a wrong result from SP_SPACEUSED, follow the below instructions to resolve this issue.

1. Run DBCC UPDATEUSAGE

2. Rebuild indexes

DBCC UPDATEUSAGE: It reports and corrects inaccurate page and row count information in catalog views. These inaccurate values may impact the result of SP_SPACEUSED.

“DBCC UPDATEUSAGE” corrects the rows, used pages, reserved pages, leaf pages and data page counts for each partition in a table or index.

This command can run over a specific database, table or index.

Example:

USE udayarumilli;
GO
DBCC UPDATEUSAGE(0);

Run DBCC UPDATEUSAGE on entire database:

USE udayarumilli;
GO

-- Running command on entire database "udayarumilli"
DBCC UPDATEUSAGE('udayarumilli');

Run DBCC UPDATEUSAGE on a specific Table:

USE udayarumilli;
GO

-- Running command on a specific table "Product_NewID"
DBCC UPDATEUSAGE('udayarumilli','[Product_NewID]');

Run DBCC UPDATEUSAGE on a specific index:

USE udayarumilli;
GO

-- Running command on a specific index "ix_Product_NewID_ID"
DBCC UPDATEUSAGE('udayarumilli','[Product_NewID]','ix_Product_NewID_ID');

Precautions:

1. It’s not supposed to run this command on frequent basis on sql instance with 2005 or later versions.

2. Can execute onetime if we find issues with SP_SPACEUSED results

3. Can schedule to execute weekly basis only if database undergoes DDL modifications.

 Have a look here for more details.

Microsoft Announced SQL Server 2014. I just came across through the below links.

Download SQL Server 2014 CTP1

What’s New in SQL Server 2014 – MSDN

  New Features Added in SQL Server 2014 by Brent Ozar

Key Features in SQL Server 2014 By Mark Worthen

Full Focus – AlwaysON in SQL Server 2014 CTP1

Creating SSIS Deployment Manifest

To demonstrate SSIS package deployment manifest I have created a test package on dummy source and destination databases. The package ETL data between source and destination databases that’s out of scope here and our intension is how to deploy a SSIS package using deployment manifest.

• Prepare you package: Make sure your package is pointing to the correct source and destination and all tasks are executing without any issue.

• Right click on project name and select properties

• In properties window go to “Deployment Utility” tab and select “True” for “Create Deployment Utility” and click on Apply.

• Now Build the project to get the deployment manifest as below

• You can check the build status at down left corner as below

• Now go to the project folder to check the deployment manifest.

• I have created the package at some test folder and I found the deployment manifest has been created infolder “/bin/Deployment/*****.SSISDeploymentManifest”

• Now we can move this package to the production server and we can deploy this package just by going through the deployment wizard as below

Deploying SSIS package using deployment manifest

• Right click on deployment manifest and click on “Deploy”

• Click on Next and choose “SQL Server Deployment” as below

• Click on Next and choose “Server Name”, Authentication type and package path. I have created a new folder and named it as “Sync_Packages” in SSIS “MSDB” folder.

• Once the package path is specified the wizard looks like this.

• Now click on next and we need not change the folder location, it can be changed if it requires.

• Click on next to deploy the package

• Just click on Finish. Connect to SSIS engine and check the package

• Now we can directly execute the package from SSMS. Just right click and Run Package.

• Click on Execute button

Working with variables in SSIS: A simple demonstration

Before building the ETL package we need create a sales history table:

CREATE TABLE Product_Sales_History(
SaleID     BIGINT      NOT NULL UNIQUE,
ProductID  VARCHAR(50) NOT NULL,
Total      INT         NOT NULL,
FYEAR      CHAR(4)     NOT NULL);

GO

Insert sample data as below.

INSERT INTO Product_Sales_History (SaleID,ProductID,Total,FYEAR)

VALUES(112889,'ELS2550',1289,2006),

(112811,'ELS2550',1289,2007),

(112812,'ELS2550',1700,2008),

(112813,'ELS2550',2400,2009),

(112814,'ELS2550',2800,2010),

(112815,'ELS2550',2918,2011),

(112816,'ELS2550',3100,2012),

(112817,'ELS2550',3000,2013);

INSERT INTO Product_Sales_History (SaleID,ProductID,Total,FYEAR)
VALUES
(112818,'DSL-14',210,2007),

(112819,'DSL-14',200,2008),

(112820,'DSL-14',189,2009),

(112821,'DSL-14',199,2010),

(112822,'DSL-14',202,2011),

(112823,'DSL-14',209,2012),

(112824,'DSL-14',304,2013);

INSERT INTO Product_Sales_History (SaleID,ProductID,Total,FYEAR)
VALUES
(112825,'AGCL-112',1210,2007),

(112826,'AGCL-112',2200,2008),

(112827,'AGCL-112',2189,2009),

(112828,'AGCL-112',2199,2010),

(112829,'AGCL-112',3202,2011),

(112830,'AGCL-112',3209,2012),

(112831,'AGCL-112',3304,2013);

go

ETL requirement: Design a ETL package to extract data from sales history to a staging table. Data needs to be loaded for the given financial year only. This financial year value will be changing.

Solution:

Create a new package and name it as “Sales_Stage_Load”.

1. Add connection managers to source and destination
2. Create a variable “Year” and assign a default value “2006”.
3. Add an “Execute SQL Task” to clean up the staging table. Map the parameter value with the variable as data needs to be cleaned for the given financial year only.
4. Add a “Data Flow” task.
5. Inside the data flow, add OLEDB source and OLEDB destination.
6. OLEDB Source: Select data from source for the given financial year. Since the value is dynamic the parameter needs to be mapped with the variable “Year”.
7. OLEDB Destination: Load data into staging table.

Implementation:

Create a package and add connection managers to source and destination.

Create a variable “Year” as below.

Add “Execute SQL Task” to the control flow and apply the properties as below.

Connection should point to the destination.

SQL statement is to delete data from stage table for the given year value.

Now MAP parameters in Parameter Mapping tab as below.

Now add a dataflow task and now the control flow looks like below.

Inside the dataflow create an OLEDB source and map it with the connection “Source”.

Data access should be “SQL Command”.

Map the parameter to the user defined parameter “Year” as below.

Map the columns as below.

Add destination and map it with the connection manager “Destination”.

Now the dataflow looks like below.

Now add “Data viewers” which can be helpful in validating the output.

Finally Dataflow looks like as below.

Execute the package:

Execution 1:

Initially the variable “Year” value is: 2006.

Now execute the package and see the output as below.

We can see there’s only one row available for the year 2006.

Execution 2:

Change the variable value to 2010.

Now execute the package and see the output as below.

We can see there are three rows available for the year 2010.

Note: This is just a sample to showcase how variables are being used in SSIS packages.

The post Using variables in SSIS – Simple example appeared first on udayarumilli.com.

Q&A

Installing SQL Server

1. What are the components installed with the SQL Server 2005 installation?

Ans:

• Server Components
• SQL Server Database Engine
• Analysis Services
• Reporting Services
• Notification Services
• Integration Services
• Client Components
• Connectivity Components
• Communication between clients and servers
• Network libraries for DB-Library, ODBC, and OLE DB.
• Management Tools
• Management Studio
• Profiler
• Configuration Manager
• Database Tuning Advisor
• Development Tools
• Business Intelligence Development Studio
• Documentation and Samples
• Books Online
• SQL Server Samples

2. What are the editions available in SQL Server 2005?

Ans:

• Enterprise Edition (32-bit and 64-bit)
• Evaluation Edition (32-bit and 64-bit)
• Standard Edition (32-bit and 64-bit)
• Workgroup Edition (32-bit and 64-bit)
• Developer Edition (32-bit and 64-bit)
• Express Edition (32-bit only)
• Compact Edition (32-bit only)
• Runtime Edition (32-bit and 64-bit)

3. What are the network protocols that SQL Server supports?

Ans:

Stand-alone named and default instances support the following network protocols:

• Shared memory
• Named pipes
• TCP/IP
• VIA

Note   Shared memory is not supported on failover clusters.

4. What are the basic software requirements for installing SQL Server 2005?

Ans:

• Microsoft Windows Installer 3.1 or later
• Microsoft Data Access Components (MDAC) 2.8 SP1 or later
• Microsoft .NET Framework 2.0 Software Development Kit (SDK)
• Microsoft .NET Framework 2.0 (Installed Automatically)
• Microsoft SQL Server Native Client (Installed Automatically)
• Microsoft SQL Server Setup support files (Installed Automatically)

5. What are the file locations for Server components?

Ans:

Server components are installed in directories with the format <instanceID>\<component name>. For example, a default or named instance with the Database Engine, Analysis Services, and Reporting Services would have the following default directories:

• <Program Files>\Microsoft SQL Server\MSSQL.1\MSSQL\ Database Engine
• <Program Files>\Microsoft SQL Server\MSSQL.2\OLAP\ for Analysis Services
• <Program Files>\Microsoft SQL Server\MSSQL.3\RS\ for Reporting Services

6. What about SSIS, Notification services and client components?

Ans:

SQL Server 2005 Integration Services, Notification Services, and client components are not instance aware and, therefore, are not assigned an instance ID. Non-instance-aware components are installed to the same directory by default: <system drive>:\Program Files\Microsoft SQL Server\90\. Changing the installation path for one shared component also changes it for the other shared components. Subsequent installations install non-instance-aware components to the same directory as the original installation.

7. List out the default path for the SQL Server components.

Ans:

Database Engine server components

\Program Files\Microsoft SQL Server\MSSQL.n\MSSQL\Binn\

Database Engine data files

\Program Files\Microsoft SQL Server\MSSQL.n\MSSQL\Data\

Analysis Services server

\Program Files\Microsoft SQL Server\MSSQL.n\OLAP\Bin\

Analysis Services data files

\Program Files\Microsoft SQL Server\MSSQL.n\OLAP\Data\

Reporting Services report server

\Program Files\Microsoft SQL Server\MSSQL.n\Reporting Services

\ReportServer\Bin\

Reporting Services report manager

\Program Files\Microsoft SQL Server\MSSQL.n\Reporting Services

\ReportManager\Bin\

SQL Server Integration Services

<Install Directory>\90\DTS\

Notification Services

<Install Directory>\90\Notification Services\

Client Components

<Install Directory>\90\Tools\

Components that are shared between all instances of SQL Server 2005

\Program Files\Microsoft SQL Server\90\Shared\

8. Can we change the directory while adding new features?

Ans:

Can’t! You must either install additional features to the directories already established by Setup, or uninstall and reinstall the product.

9. What are the log files generated while Installing\Upgrading\Applying (packages) SQL Server on Windows machine? (SQL Server 2008 / R2)

Ans:

Summary.txt (SQL 2005)

This file shows the SQL Server components that were detected during Setup, the operating system environment, command-line parameter values if they are specified, and the overall status of each MSI/MSP that was executed.

Location:

%programfiles%\Microsoft SQL Server\100\Setup Bootstrap\Log\.

Note:

To find errors in the summary text file, search the file by using the “error” or “failed” keywords.

Summary_engine-base_YYYYMMDD_HHMMss.txt

Generated during the main workflow

Location:

%programfiles%\Microsoft SQL Server\100\Setup Bootstrap

\Log\<YYYYMMDD_HHMM>\

Summary_engine-base_YYYYMMDD_HHMMss_ComponentUpdate.txt

Generated during the component update workflow.

Location:

%programfiles%\Microsoft SQL Server\100\Setup Bootstrap\Log\<YYYYMMDD_HHMM>\

Summary_engine-base_20080503_040551_GlobalRules.txt

Generated during the global rules workflow.

Location:

%programfiles%\Microsoft SQL Server\100\Setup Bootstrap\Log\<YYYYMMDD_HHMM>\

Detail.txt

Detail.txt is generated for the main workflow such as install or upgrade, and provides the details of the execution. The logs in the file are generated based on the time when each action for the installation was invoked, and show the order in which the actions were executed, and their dependencies.

Location

%\Microsoft SQL Server\100\Setup Bootstrap\Log

\<YYYYMMDD_HHMM>\Detail.txt.

Note:

If an error occurs during the Setup process, the exception or error are logged at the end of this file. To find the errors in this file, first examine the end of the file followed by a search of the file for the “error” or “exception” keywords.

Detail_ComponentUpdate.txt

Detail_GlobalRules.txt

MSI log files

The MSI log files provide details of the installation package process. They are generated by the MSIEXEC during the installation of the specified package.

Location

%programfiles%\Microsoft SQL Server\100\Setup Bootstrap\Log \<YYYYMMDD_HHMM>\<Name>.log.

Note:

At the end of the file is a summary of the execution which includes the success or failure status and properties. To find the error in the MSI file, search for “value 3” and usually the errors can be found close to the string.

ConfigurationFile.ini

The configuration file contains the input settings that are provided during installation. It can be used to restart the installation without having to enter the settings manually. However, passwords for the accounts, PID, and some parameters are not saved in the configuration file.

Location:

%programfiles%\Microsoft SQL Server\100\Setup Bootstrap\Log\

<YYYYMMDD_HHMM>\

SystemConfigurationCheck_Report.htm

Contains a short description for each executed rule, and the execution status.

Location:

%programfiles%\Microsoft SQL Server\100\Setup Bootstrap\Log

\<YYYYMMDD_HHMM>\

10. How much had disk space required installing the SQL Server 2005/08?

Ans:

2 GB. Before the installation is started windows installer allocated 2 GB of temporary space for installation.

11. What is the space required for each component in SQL Server?

Ans:

Database Engine and data files, Replication, and Full-Text Search – 280 MB

Analysis Services and data files – 90 MB

Reporting Services and Report Manager – 120 MB

Notification Services engine components, client components, and rules components – 50 MB

Integration Services – 120 MB

Client Components – 850 MB

SQL Server Books Online and SQL Server Compact Edition Books Online – 240 MB

Samples and sample databases - 410 MB

(Note that samples and sample databases are not installed by default.)

12. List out the Windows machines which supports the SQL Server 2005 Enterprise edition.

Ans:

32-Bit:

Windows 2000 Server SP4

Windows 2000 Advanced Server SP4

Windows 2000 Datacenter Edition SP4

Windows Server 2003 Server SP1

Windows Server 2003 Enterprise Edition SP1

Windows Server 2003 Datacenter Edition SP1

Windows Small Business Server 2003 Standard Edition SP1

Windows Small Business Server 2003 Premium Edition SP1

Windows Server 2008 Standard (32 bit and 64 bit)

Windows Server 2008 Enterprise (32 bit and 64 bit)

Windows Server 2008 Data Center (32 bit and 64 bit)

Windows Server 2008 Web Edition (32 bit and 64 bit)

64-Bit:

Windows Server 2003 64-Bit Itanium Datacenter Edition SP1

Windows Server 2003 64-Bit Itanium Enterprise Edition SP1

Windows Server 2008 Itanium

13. What are the security considerations for a SQL Server installation?

Ans:

Before Installation:

• Enhance physical security
• Use firewalls
• Isolate services
• Create service accounts with least privileges
• Disable NetBIOS and server message block

After Installation:

• Run SQL Server services with the lowest possible privileges.
• Associate SQL Server services with Windows accounts.
• Use Windows Authentication for connections to SQL Server.
• Always assign a strong password to the sql account.
• Always enable password policy checking.

14. What additional software requires for installing SSRS 2005?

Ans:

• Microsoft Internet Information Services (IIS) 5.0 or later is required for Reporting Services installations.
• Microsoft Internet Explorer 6.0 SP1 is required for installations of the Report Designer component of Reporting Services.

15. Which component performs the configuration check while installing the SQL Server 2005?

Ans:

As part of SQL Server 2005 Setup, the System Configuration Checker (SCC) scans the computer where Microsoft SQL Server 2005 will be installed. The SCC checks for conditions that prevent a successful SQL Server installation. Before Setup starts the SQL Server 2005 Installation Wizard, the SCC retrieves the status of each check item, compares the result with required conditions, and provides guidance for removal of blocking issues. All of the SCC check items are network enabled; checks can run on a local computer, as well as in remote and cluster situations.

16. What are the precautions needs to be taken before installing SQL Server 2005?

Ans:

• Be sure the computer meets the system requirements for SQL Server 2005
• Review Security Considerations for a SQL Server Installation.
• Run SCC to identify the blocking issues and resolve before go ahead.
• Make sure you have administrator permissions on the computer where SQL Server will be installed. If you install SQL Server from a remote share, you must use a domain account that has read and execute permissions on the remote share.
• Back up your current installation of SQL Server if you are running an instance of SQL Server on the computer where SQL Server 2005 is to be installed
• Verify that the disk where SQL Server will be installed is uncompressed. If you attempt to install SQL Server to a compressed drive, Setup will fail
• Exit antivirus software while installing SQL Server
• Stop all services that depend on SQL Server, including any service using Open Database Connectivity (ODBC), such as Internet Information Services (IIS). Exit Event Viewer and registry editors (Regedit.exe or Regedt32.exe).

17. List out the Instance-Aware and Instance-Unaware Services

Ans:

Instance-aware services in Microsoft SQL Server 2005 include:

• SQL Server
• SQL Server Agent
• Analysis Services
• Reporting Services
• Full-Text Search

Instance-unaware services in SQL Server 2005 include:

• Notification Services
• Integration Services
• SQL Server Browser
• SQL Server Active Directory Helper
• SQL Writer

18. What is the installation log file location for SQL Server 2005?

Ans:

Summary.txt:

C:\Program Files\Microsoft SQL Server\90\Setup Bootstrap\LOG

All other files:

C:\Program Files\Microsoft SQL Server\90\Setup Bootstrap\LOG\Files

Here you find logs for each individual component as well as the actions performed at the time of installation.

19. What information stored in Summary.txt?

Ans:

This file has information on the installation start and stop time, installed components, machine name, product, version and detailed log files.  Although this file differs slightly based on selected installation components, this file does not have any user names, passwords, service accounts, ports, etc.  What this file does have is references to the detailed files which will be reviewed next.

20. Is there any possibility to find out the “sa” password from log files?

Ans:

Clear Passwords not stored at anywhere. But !

When it comes to clear text passwords being stored in the detailed log files, it appears as if the sa password validation and confirmation is logged, but the actual password is never stored in clear text during the database services installation.  As an example, the files listed below reference the usage of the sa password:

• SQLSetup0002_MachineName_SQL.log
• SQLSetup0002_MachineName_Tools.log
• SQLSetup0002_MachineName_WI.log

Stored in C:\Program Files\Microsoft SQL Server\90\Setup Bootstrap\LOG\Files

After reviewing the SQL Server 2005 installation log files, it appears as if temporary files are referenced.  Do these local files have clear text passwords?  Based on files located at the below location C:\DOCUME~1\ProfileName\LOCALS~1\Temp\*.tmp these files appear to be cleaned up after the installation process and do not appear to pose any additional vulnerability because they do not appear to have the passwords in clear text.

21. What are the prerequisites for installing SQL Server 2008?

Ans:

Microsoft SQL Server 2008 setup requires Windows Installer 4.5 and .Net Framework 3.5 SP1 to be installed. The Windows Installer 4.5 and .Net Framework 3.5 SP1 can be installed independently or it can be installed by double clicking SETUP.EXE within SQL Server 2008 installation media. Both Windows Installer 4.5 and .Net Framework setups are also available in <Drive>:\x86\redist folder of installation media. Once Windows Installer 4.5 and .Net Framework 3.5 SP1 is installed the system requires a restart of the operating system.

22. I have applied SP3 on 2005 instances. Where we can find the log files?

Ans:

C:\Program Files\Microsoft SQL Server\90\Setup Bootstrap

\LOG\Hotfix\Summary.txt (On that day)

Other files like component wise files are also located in the same folder.

23. What is Slipstreaming?

Ans:

It is a term used to describe merging original source media with updates in memory and then installing the updated files. Slipstreaming has been supported by Windows Operating systems for awhile but has just been added to SQL Server 2008 service pack 1. Slipstream allows you to go to the latest and greatest, currently service pack 1 and a CU for service pack 1. Prior to service pack, we supported just update the setup file also referred to as “Patchable Setup”. Since the release of SQL Server 2008 Service Pack 1, it is recommend to use the slipstream procedures instead as patchable setup since the entire product can be updated and you will be using the latest and greatest. Any scenario (install, upgrade, addnode) that is supported by the original media is supported when slipstream.

25. I have installed SQL 2008 Database Engine component to an instance and now I want to add features to this instance using slipstream. How do I add features to an existing instance?

Ans:

In theory you just run the slipstream build again to add features. However, setup will fail since setup does not correct detect that it is installed and needs to be patched versus installed.  In this case, you need to add features using original media and then patch using the service pack installer. We don’t support features within an instance at different levels, so ensure features within an instance are at the same patch level.

26. I have slipstreamed media, but I just want to install the original media (RTM). How can I just install the original media?

Ans:

You need to use your original media.

27. What if I did not copy the ia64 and x64 folders to my original media which is necessary for slipstreaming. Can I still install x86?

Ans:

Technically, it will work. But we do not recommend skipping merging all architectures since at some point, a user might install one of these architectures.  If you merges x86 but not x64, you media is inconsistent. If at a later point in time, you run x64, the result will be unpredictable.

28.I already have SQL Server 2008 instance and now I want to update to service pack 1. Do I need to use slipstream?

Ans:

No, slipstream will not work when the product is already installed.

29. Does PCUSource need to be an absolute path?

Ans:

No, it can be a relative path, such as “.\PCU”. However, when you launch setup.exe your current path needs to point to the setup.exe.

**30. I am hitting the error: “The setting ‘PCUSOURCE’ specified is not recognized.”

Ans:

If you have followed the slipstream instructions, ensure the path to PCUSOURCE does not contain spaces. The setup does not handle the spaces as expected.  The quick workaround is to rename the PCUSource path so it does not contain any spaces. You can confirm this is the problem by viewing the Detail_ComponentUpdate.log located at %programfiles%\Microsoft SQL Server\100\Setup Bootstrap\Log\<last session>. Search for “PCUSource”. If you see commas in the PCUSource path, this is the issue:

31: Can I slipstream in any CU?

Ans:

In general, yes.  However, you need to ensure the CU will work the original release (RTM) or SP.  For example, if you are slipstreaming Service Package 1 (SP1), then only CUs based on SP1 can be slipstreamed into the installation. If you are not slipstreaming a service pack, then you need to ensure the CU is for the original release.

Uninstalling the Service Pack:

32. After I slipstream the original media and service pack 1, and then uninstall the service pack is it the same as just install the original media?

Ans:

Essentially, it is the same. However some of the components (e.g. SNAC, MSXML 6, and Setup support files) can’t be rolled back. The core features: Database Engine, Reporting Services, Analysis Services, and the other shred components will be rolled back.

33. Can I use slipstream to upgrade from SQL 2005 to SQL Server 2008?

Answer: Yes.

34. Can I use slipstream to upgrade from SQL 2000 to SQL Server 2008?

Answer: Yes.

35.  Is there a way to find out when a patch / sp was last applied to an instance?

Ans:

• Start SSMS, open help menu and go to “about”
• Run Select @@version
• Run SELECT SERVERPROPERTY(‘productversion’), SERVERPROPERTY (‘productlevel’), SERVERPROPERTY (‘edition’)
• Run XP_READERRORLOG and from the result set we can find the version details
• If nothing worked as far as I know only option there would be to look at the add/remove programs list (or dump this data from the registry to make it easier to deal with) and get that info from there. SQL Server doesn’t track that within the system databases.

36. Can you identify the current version from version no?

Ans:

Yes we can!

Version Latest

2008R2 SP1 – 10.50.2 —.-

2008R2 RTM – 10.50.1 —.-

2008 SP3 – 10.00.5.—

2008 SP2 – 10.00.4.—

2008 SP1 – 10.00.2.—

2008 RTM – 10.00.1.—

2005 SP4 – 9.00.5.—

2005 SP3 – 9.00.4.—

2005 SP2 – 9.00.3.—

2005 SP1 – 9.00.2.—

2005 RTM – 9.00.1.—

2000 SP4 – 8.00.7—-

Errors While Installing…………………….

1. Can you narrate one critical installation issue that you resolved?

Ans:

Yes we have few.

A) I have got a request to install SQL Server 2005 Standard Edition with SP4. While installing database services it suddenly failed by throwing a pop – up. The error message:

“The SQL Server service failed to start. For more information, see the SQL Server Books Online topics, “How to: View SQL Server 2005 Setup Log Files” and “Starting SQL Server Manually”

Ans:

I gone through the all security credentials and found everything is fine. Gone through the log files and found the windows server is running with 24 processors Where as SQL Server 2005 Standard Edition supports upto 4 processors. To resolve the issue follow the steps below.

1. Update windows config to use only one processor (From MSConfig — IniBoot)

2. Restart the windows server

3. Install SQL Server

4. Apply Service Pack 4

5. Change config to use default configuration

6. Restart the windows server

B) Installed failed on MSXML 6 Service Pack 2”

Ans:

Remove the MSXML 6.0 Parser and related components (with MSXML 6 *.*) from Add and Remove Programs at Control Panel. I was not able to remove it. I found there is a solution to force removal of this component nothing but windows installer cleanup.

We can get it from MSDN download center or we can get it from below link

http://www.eStockCard.com/Software/msicuu2.exe . Once all related components of MSXML 6.0 Parser were removed I ran the setup again and it was completed w/o any issue.

Other Issues:

1 Sample Error from errorlog–>MSI (s) (C4:C8) [19:04:30:953]: Product: Microsoft Office 2003 Web Components — Error 1706. Setup cannot find the required files. Check your connection to the network, or CD-ROM drive. For other potential solutions to this problem, see

C:\Program Files\Microsoft Office\OFFICE11\1033\SETUP.CHM.

Ans:

Solution 1: Uninstall SQL server 2005 completely and then try to manually run the OWC11.msi file available in Tools folder of sql 2005.Then try to install sql 2005 freshly !

Solution 2: Just uninstall Office web components from Add \ Remove programs and then try to install sql 2005

2. “There was an unexpected failure during the setup wizard” – Error 1603

Ans:

Solution1: To work around this problem, set the folders in the correct layout for the SQL Server 2005 installation. The SQL Server 2005 installation uses the following two folders:

• Servers
• Tools

These two folders must be under the same level of a folder or the root folder of a drive. The names of these folders must be exactly Servers and Tools. The Servers folder contains all the files that are required to install major SQL Server 2005 components, such as database engine. The Tools folder contains tools components and Books Online for SQL Server 2005.Then try installing sql from the path\servers\setup.exe

3. SP2 fails to install database services – MSP Error: 29512 “Unable to install Windows Installer MSP file” Error Snippet : MSP Error: 29512 SQL Server Setup was unable add user Clusteruser@FQDN (where FQDN is the actual fully qualified domain name – abbreviated here for security) to local group DOMAIN\SQL2005SQLAgents (where DOMAIN is the actual name of the domain). MSP returned 1603: A fatal error occurred during installation.

Ans:

Solution: KB 926622 — This article is for SP1 and also applicable to SP2 also.
To install SP2, try creating the following path, and restart SP2 setup:
DRIVE:\Microsoft SQL Server\MSSQL.2\MSSQL\FTData

4. SQL Server 2005 Setup program taking very long time to be completed

Ans:

Reason1: This problem may occur when you install software that also installs SQL Server 2005, such as Microsoft System Center Data Protection Manager (DPM) 2007.

Reason2: When the primary domain has many external trust relationships with other domains, or when many lookups are performed at the same time, the time that is required to look up domain group names may increase significantly. Therefore, the time that is required to install SQL Server 2005 may also increase.

Solution1: This problem can be solved by installing a Hotfix. Below is the link for the Hotfix.

http://support.microsoft.com/?kbid=910070

5. MSP Error: 29538 SQL Server Setup did not have the administrator permissions required to rename a file Sample Error

Product : Database Services (MSSQLSERVER)
Product Version (Previous) : 1399
Product Version (Final) :
Status : Failure
Log File : C:\Program Files\Microsoft SQL Server\90\Setup Bootstrap\LOG\Hotfix\SQL9_Hotfix_KB921896_sqlrun_sql.msp.log
Error Number : 29538
Error Description : MSP Error: 29538 SQL Server Setup did not have the administrator permissions required to rename a file: C:\Program Files\Microsoft SQL Server\MSSQL\Data\mssqlsystemresource1.ldf. To continue, verify that the file exists, and either grant administrator permissions to the account currently running Setup or log in with an administrator account. Then run SQL Server Setup again

Ans:

You can run the install in repair mode and repair your RTM instance. After that, you should be able to install SP2. Take a look at Books Online or template.ini on the original media for repair mode options. Here’s a sample snippet from template.ini to repair all files, reg keys, and shortcuts for a default instance.

start /wait setup.exe /qb INSTANCENAME=MSSQLSERVER REBUILDDATABASE=1 REINSTALL=All SAPWD= REINSTALLMODE=OMUS

6. SQLEXpress installation error

“An instance with the same name is already installed on this computer. To proceed with SQL Server Setup, provide a unique instance name.”

Solution:

You can get this error if your previous uninstallation of SQLExpress doesn’t get uninstalled properly. You need to cleanup some registry keys to proceed with the installation of SQLExpress. For more information http://blogs.msdn.com/b/astebner/archive/2005/12/08/501885.aspx

7. Error MSP Error: 29537 while installing SQL Server 2005 SP3

Sample Error

Product                   : Database Services (MSSQLSERVER)
Product Version (Previous): 4035
Product Version (Final)   :
Status                    : Failure
Log File                  : C:\Program Files\Microsoft SQL Server\90\Setup Bootstrap\LOG\Hotfix\SQL9_Hotfix_KB955706_sqlrun_sql.msp.log
Error Number              : 29537

Error Description         : MSP Error: 29537  SQL Server Setup has encountered the following problem: [Microsoft][SQL Native Client][SQL Server]CREATE DATABASE failed. Some file names listed could not be created. Check related errors.. To continue, correct the problem, and then run SQL Server Setup again.

Ans:

CAUSE:
By default the setup creates the Temp_MS_AgentSigningCertificate_database Database on specified default database location, If the location doesn’t exist, it fails to create the database and the setup fails.

RESOLUTION:

1. In SSMS, go to Server Properties > Database Settings > Database Default
Locations , check default location for Data and Log .
2. Try to access locations specified at Data and Log, Make sure files are available
there.
3. If any of the files missing from above location , we hit the above error.
4. In that case, change the path to point to reall location of mdf/ldf files .
5. Setup should now succeed.

8. “Error 1706. Setup cannot find the required files.

Check your connection to the network, or CD‐ROM drive”

Sol:

Just uninstall Office web components from Add \ Remove programs

and then try to install sql 2005

9. “There was an unexpected failure during the setup wizard” ‐ Error 1603

Sol

Set the folders in the correct layout for the SQL Server 2005 installation. The SQL Server 2005 installation uses the following two folders:

• Servers

• Tools

These two folders must be under the same level of a folder or the root folder of a drive. The names of these folders must be exactly Servers and Tools.

The post Installing SQL Server appeared first on udayarumilli.com.

Q&A

Upgrading SQL Server

1. Can you upgrade SQL Server 2008 SP2 Standard Edition to 2008 R2 Developer Edition?

Ans:

You can’t change the version of the installed instance as far as I know, but you could install a second instance with the Dev edition, or uninstall the Standard edition, install Developer edition and attach the user databases.

2. Does upgrade advisor analyze the remote instances?

Ans:

Upgrade Advisor can analyze remote instances of SQL Server, except for SQL Server Reporting Services. To analyze Reporting Services, Upgrade Advisor must be installed and executed on the report server.

3. Ho to upgrade a SQL Server 2000 to SQL Server 2008?

Ans:

That said, what kind of upgrade are you doing? Are you planning an in-place or side-by-side upgrade? The different approaches will result in different checklists. The safest approach is the side-by-side upgrade. You can do this either by using a backup and restore or dettach/attach of the database files. I’d suggest using the backup & restore as the safer approach. Here are the things I’d do:

• Run Upgrade Analysis tool from Microsoft. Address any issues raised there, first.
• Identify DTS packages. These must be migrated by hand, unless you buy PragmaticWorks excellent software. Rebuild the DTS packages as SSIS.
• Script out all SQL Agent jobs.
• Script out all security
• Backup the systems and validate the backups (preferably by restoring them to another system)
• Run the security script on the new system
• Run the restore on the new system.
• Validate the databases by running DBCC
• Manually update all statistics
• Run the SQL Agent script

4. Have you ever prepared a checklist while performing an upgrade?

Ans:

Yes Of course!!!

• Identify which databases need to be upgraded (ie are still on older versions of SQL Server)
• Of those databases, which are not supported on more recent versions of SQL Server?  This is one for the appropriate vendor – so do we have contact details for the vendor?
• Of those non-supported databases, if this is just because the vendor hasn’t tried it, are we able to try and will they support is in our efforts?
• Identify maintenance routines and scheduled jobs associated with database
• Identify dependencies upon older technologies (eg DTS rather than SSIS), and work out an upgrade path for these
• What applications depend upon the database?
• What UserIDs are required?
• How do we configure the application to point to a new database?
• What else needs to be changed?  (eg middleware servers)
• Are parts of the database subject to Replication?
• Is the database part of a Log Shipping routine?
• Is the database part of a Mirror set?
• What’s the recovery plan for the database?
• What’s the backup plan for the database?
• Are there any SSRS jobs relating to this database?
  • What are they?
  • Where are they?
  • How do we migrate these across?
  • What else depends upon those reports?
• …and similarly, are there any OLAP / SSAS dependencies?

It might also be worth thinking about the amount of data in the database:

• How much data have we got?
• How fast is the database growing?
• For how long do we need to retain this data?
• Can we archive anything off to improve performance?

Of course, all the above forms part of your database documentation, so it should be easily to hand, right?

The other things to work out include:

• How do we test this thing to ensure the migration is successful?
• How do we rollback if it isn’t successful?
• Point of contact for the supplier / vendor / development team
• Point of contact for the customer(s) / user(s)

5. Can you detach a SQL Server 2005 database and attach it to a SQL Server 2008 server?

Ans:

Yes. SQL Server 2005 databases are compatible with SQL Server 2008. However, that attaching a SQL Server 2005 database to SQL Server 2008 automatically upgrades the SQL Server 2005 database to a SQL Server 2008 database and the database is then no longer usable by the SQL Server 2005 installation.

6. Can you detach a SQL Server 2008 database and attach it to a SQL Server 2005 server?
Ans:

No. The only way to move a SQL Server 2008 database to a SQL Server 2005 server is by transferring the data using a method such as Data Transformation Services (Import/Export),SSIS, bcp, or use of a query between linked servers.

7. How long will it take to upgrade my SQL Server databases?

Ans:

Many factors affect the amount of time needed to upgrade SQL Server Databases. Depending on the complexity of each database, Size of databases, the hardware platform, number of processors, disk subsystem, and amount of RAM plays a significant part in the amount of time required for the upgrade. Selecting “data validation” during the setup increases the amount of time needed to perform the upgrade by a factor of two. Some typical times for the upgrade process are:

8. When you upgrade a SQL Server, the upgrade wizard seems to stop responding and fails. Why?

Ans:

If applications or services have open ODBC connections to the SQL Server 2005 server during the conversion process, they may not allow the SQL Server to shut down completely. The conversion process will not proceed on to the next step if it does not receive verification that the SQL Server has been completely stopped.

9. “I’m trying to restore a 25 GB database backup taken from a Windows 2003/SQL 2005 machine to a Windows 2008/SQL 2008 machine in the Amazon EC2 cloud, using a .bak file and the SQL Management Studio. SQL Management Studio reports the restore reaches 100% complete, and then just hangs indefinitely (24+ hours) using a lot of CPU, until I restart the SQL Server service. Upon restart, SQL again uses a lot of CPU activity for what seems to be an indefinite amount of time, but the DB never comes online.”

Ans:

The database is in the process of being upgraded from SQL 2005 to SQL 2008 when you kill it. Check the ERRORLOG in SQL Server and you should see that the database restore is complete and that the database is being upgraded.

This process is normally very quick, but it can take a while to perform depending on the database, especially if you have a lot of pending transactions in the database which much be rolled forward or backward before the database can be upgraded.

9. How to rollback the upgrade?

Ans:

If the legacy SQL Server instance is replaced by a new SQL Server 2008 instance, rolling back an in-place upgrade can be complex and time-consuming, whereas in a side-by-side upgrade the legacy instance remains available if a rollback is needed.

10. What are the different ways in upgrading to a higher version?

Ans:

There are two ways:

In-Place Upgrade: Installs 2008 and overwrite on the 2005 Server.

Side-by-side Upgrade: A new instance will be installed and moves the databases.

11. Give some examples when we consider Side-by-side and In-Place?

Ans:

Pros & Cons: In-Place

Pros

• Easier, mostly automated
• Generally fast overall process
• Requires no additional hardware
• Applications remain pointing to same server/database name

Cons

• Less granular control over upgrade process
• Instance remains offline during part of upgrade
• Not best practice for all components
• Complex rollback strategy
• Not recommended for SSAS

Pros & Cons: Side-by-side:

Pros

• More granular control over the upgrade process
• Original database left unchanged; allows for testing of new database
• Single occurrence of database downtime
• Relatively straightforward rollback strategy

Cons:

• Usually require additional hardware
• Server/database name changes
• Not practical for VLDB unless utilizing SAN(Beware of “loss of quick roll-back)

12 What are the parameters should be considered while choosing the upgrade process?

Ans:

Components: A certain upgrade strategy might not be possible because the component does not support it. For example, there is no in-place upgrade for SSIS from SQL Server 2000; Microsoft recommends that you upgrade most SQL Server 2000 SSAS components.

Versions and Editions: The in-place upgrade strategy does not support all paths between versions and editions. For example, to upgrade a SQL Server 2000 Enterprise Edition instance to SQL Server 2008 Standard Edition, you must perform a side-by-side upgrade because SQL Server Setup does not support an in-place upgrade path.

Partial upgrading: To transition only a few databases on a server to SQL Server 2008 and leave the rest on the legacy version, you must use a side-by-side upgrade.

Upgrading over time: To transition databases gradually, a few databases at a time, from a legacy instance to SQL Server 2008, you can only use a side-by-side upgrade.

Effect on applications: If your organization requires minimal disturbance to the existing applications and users, you may want to choose an in-place upgrade if possible.

Availability: Both an in-place upgrade and a side-by-side upgrade require that the databases be unavailable for a certain amount of time. The amount of downtime required depends primarily on the size of the data sets. At first, it might seem that an in-place upgrade would be faster than a side-by-side upgrade because the data is not transferred from one server to another. However, an in-place upgrade also requires time for the installation of SQL Server 2008. In a side-by-side upgrade, SQL Server 2008 is already installed on another instance. If the data transfer proceeds quickly and few changes are needed on the new instance, a side-by-side upgrade might be faster than an in-place upgrade.

13. We have upgraded databases from SQL Server 2000 to SQL Server 2008 and now the upgrade hits the production. Unfortunately a part of application is not supporting SQL Server 2008. Do we need to Rollback entire process to SQL 2000? Is that the only solution? If it is the only way! Since the databases at production transactions are being running and the data has been updated. Please assist us.

Ans

However, after the upgraded SQL Server 2008 instance goes into production and starts capturing new data, there will come a point in time when enough new data has been captured that a rollback is no longer realistic. For an in-place upgrade, if you encounter problems after the system is in production, making adjustments or “patches” to the new application would be a better option than attempting a rollback. For a side-by-side upgrade, you could employ SSIS to transfer new data from the SQL Server 2008 instance to the legacy SQL Server 2000 to bring it current. Depending on the complexity of the data, this could be a difficult process.

14. Can you list out some of the compatibility options while upgrading?

Ans:

For example we goanna upgrade SQL 2000 to SQL 2008:

• Some features do not exist anymore
• Examples: undocumented system stored procedures, DUMP, LOAD, sp_addalias,
• Some are deprecated, Will be removed in future versions of SQL Server
• Examples: SQL Mail, COMPUTE BY, Remote Servers, backup passwords,…
• Some features behave differently
• Example: Access to catalog views (new security on system views)
• Some editions have different features
• Example: Express has no SQL Server Agent

15. What are the different tools available while upgrading from SQL 2000 to SQL 2008?

Ans:

Primary Tools:

• SQL Server 2008 Upgrade Advisor
• DTS xChange

Secondary Tools

• Microsoft® Assessment and Planning Toolkit 3.2
• SQL Server 2008 Upgrade Assistant
• SQL Server Best Practices Analyzer
• System Configuration Checker
• SQL Server Profiler
• SQL Server: Deprecated Features Object Counter
• Other tools

16. Error while upgrading to SQL server 2005 from Sql server 2000.

“while upgrading my sqlserver 2000 with version 8.0.2039 to SQLserver 2005, msxml6.msi failed to upgrade and while trying to uninstall it is try to look the msi file which missing from the path”

Ans:

MSXML 6 services installed in my server is a lower version of SP2 msxml6-KB954459 and not allowing the upgrade, because setup trying to upgrade MSXML6.MSI and it could not locate the file in the previous installation and Of course it got missed.

So, we have worked out here to download the same version from Microsoft website and then extracted the MSXML6.MSI file to some location and then we tried to un-install the MSXMl service and it went successfully.

Later, again we have installed the msxml6-KB954459-enu-x86.exe and upgrade of SQLserver 2000 to 2005 went smooth without issues and applied latest servicepack 4 successfully.

17. How to Upgrade to SQL SERVER 2005?

Ans:

• We can directly upgrade instances of SQL Server 2000 Service Pack 3 (SP3) or later, and instances of SQL Server 7.0 SP4 or later, to SQL Server 2005. We can perform most upgrade operations through Setup
• Before running Setup to upgrade to SQL Server 2005, we should first review system requirements and update Matrix
• Before beginning an upgrade
• All SQL Server database files will have to be backed up.
• Appropriate DBCC commands should be run to ensure consistent state.
• SQL Server System databases will have to be configured with autogrow setting to ensure that they will have adequate disk space.
• All startup procedures will have to be disabled; else they will block the process of upgrading.
• Replication log should be emptied and Replication will have to be stopped.

• Another factor that needs to be taken into account while preparing for an upgrade, are the features that have been deprecated in SQL Server 2005.
• Once all the above has been done, SQL Server 2005 setup has to be run and the instance installed.
• The upgrade Advisor does not get installed automatically when SQL Server is installed. It has to be installed separately.
• After reviewing system requirements and upgrade Matrix, run SQL Server Upgrade Advisor to analyze the instances of SQL Server 2000 and SQL Server 7.0.
• Upgrade Advisor produces lists of issues that we must fix before or after upgrading. SQL Server Setup will detect blocking issues that will prevent us from upgrading to SQL Server 2005 (The table alias should not be used in order by clause)
• Thereafter, move user databases to the instance by using backup and restore or detach and attach functionalities in SQL Server 2005. Then register the server, repopulate full text catalogs, update the statistics and run Surface Area Configuration tool. Change the compatibility level to 90 from 80

18. What are the issues u faced in sql server upgrade?

Ans:

Common causes

• SQL Server or the machine running the upgrade loses its network connection.
• The database in which you were working has run out of log or data space.
• You are not allowed to perform an update to a table.
• The database is corrupted.
• The database is not available (still in recovery.) It may be unavailable if the upgrade program begins to work before SQL Server finishes performing recovery after startup.
• Unable to restart the server

Can identify the issue from the upgrade log files and resolve the issues and rerun the upgrade advisor

19. What is the sequence to install service packs or hotfixes on an instance of SQL Server that is part of Log Shipping/Database Mirroring/Replication/Failover Clustering environment?

Ans:

When an instance of SQL Server is configured as part of Log Shipping, Database Mirroring, Replication, or Failover Clustering environment, it is important to install service packs or hotfixes in a correct sequence otherwise we may get unexpected issues.

Log Shipping:

There is no required sequence to apply a service pack or hotfix for Primary, Secondary and Monitor servers in a Log Shipping environment. The following is my preferable to apply service pack or hotfix:

• Apply the service pack or hotfix on the Monitor server.
• Apply the service pack or hotfix on the all Secondary servers.
• Apply the service pack or hotfix on the Primary server.

Database Mirroring:

If you install service packs or hotfixes on servers in a database mirroring environment, you need to determine the role of the servers. If there are many mirroring sessions configured on the server, you need to determine all possible roles that could be. For instance, if the server is acting as a mirror server for any database mirroring session, update the server as the mirror role for all mirroring sessions. To do this, follow these steps:

• If a witness server is configured in the database mirroring session, disable the automatic failover during the update process. To do this, remove the witness server from the mirroring session.
• If the safety level of the database mirroring session is OFF (asynchronous mode), change the safety level to FULL (this is required in step 3).
• Make sure all database mirroring sessions to be in Synchronous mode and synchronized.
• Pause the database mirroring sessions that are present on the server.
• Install the service pack or hotfix on the mirror server.
• Resume the database mirroring sessions.
• Perform manual failover (all the mirroring sessions on this principal server) to the mirror server so that mirroring server assumes the principal role.
• Pause the database mirroring sessions as step 4.
• Install the service pack or hotfix on the new mirror server (previous principal server).
• Resume the database mirroring sessions.
• If you changed the safety level in step 2, change the safety level back to OFF.
• If the database mirroring session has a witness server, undo the changes made in step 1.

Replication:

In a replication environment, there is no preferable sequence to apply service pack or hotfix for non-bidirectional replication typology. However, for bi-directional replication typology such as merge typology or transactional replication with updateable subscriptions, you must upgrade Distributor, Publisher, and Subscribers in the following order:

• Apply the service pack or hotfix on the Distributor server.
• Apply the service pack or hotfix on the Publisher server.
• Apply the service pack or hotfix on the Subscriber server.

 Failover Clustering:

In SQL Server 2005, if you want to install a service pack or hotfix, you must install the setup on the Active node (node that currently runs SQL Server services). When running the setup which will launch simultaneously “remote silence” on all passive nodes.

However, in SQL Server 2008 and SQL Server 2008 R2, the service pack or hotfix deployment is changed to reduce the downtime. Now, you must install the service pack or hotfix on the passive node first. To do this, following these steps:

• Apply the service pack or hotfix on the passive node (or all passive nodes if you have more than one).
• Reboot the passive node.
• Failover the SQL Server failover cluster to the passive node (and the passive node becomes active now).
• Apply the service pack or hotfix on the new passive node (previous active node).
• Reboot the passive node.

The post Upgrading SQL Server appeared first on udayarumilli.com.

Hello All, I have been collecting interview questions from the people who given interviews at various organizations. Below are the list of questions. It includes, SQL DBA, MSBI, SQL Developer, SQL Server.

1

​

SSRS:
1. How to render a report to a user email?
2. How to join two datasets and use in a single report?
3. How to do paging in SSRS?
4. How to deal with multi valued parameters?
5. I want one page should be displayed in landscape and other pages in different formats in a report. Can you design a SSRS report for this requirement?
6. How to tune the performance of SSRS report?
7. How to design a Drilldown report?
8. What is the difference between Table and Matrix?

SSIS:
1. Design a SSIS package for the following requirement. Create a table, load data and move to the different schema using SSIS.
2. Are you following any framework for ssis?
3. How to execute parent and child ssis packages? Locate 1000 files location?
4. How to add users to a database using SSIS?
5. Which tasks should be used to import a million records txt files?
6. What are the configuration options for parent child packages?
7. What is the new configuration option added in SQL Server 2012?
8. What is the difference between “Execute SQL” and “Execute T-SQL” tasks?

T-SQL:
1. Why we can’t put Order by inside the view?

2

1. How to call a web service from SSIS?
2. What are the performance issues you have faced in SSIS?
3. Why SSIS? What is the use of ETL?
4. What is difference between SSIS and SSAS?

5. What is a dimensional databases?

6. Difference between Dim and Relational?
7. What is a cross apply and how to use this?
8. How to handle a result set from a webservice or Execute SQL task?

3

!. What is a surrogate keys? How to call a unique column in dimension?
2. I have a table
Customer    Book
C1               B1
C2               B1
C3               B1

I need output: All combination of all customers. Only distinct values

Example:

Customers
C1,C2
C1,C3
C2,C3

3. Can we use more than one CTE in a single select query?
4. We have three tables (Customer, Targets and Sale tables)

Customer – CID, CName
Targets – TID, CID, Target_Amt
Sale – SAID, CID, Sale_Amt

I need an output as below:

CID, CName, Total_Target_Value, Total_Sale_Value

;WITH CTE AS (
select t.cid,sum(t.target_amt) as targets
from targets t
group by t.cid)
select    c.cid,
c.cname,
ct.targets AS ‘Total_Target_Value’,
sum(s.sale_amt) as ‘Total_Sale_Value’
from customer c
INNER JOIN SALE S on S.cid=c.cid
INNER JOIN cte ct on ct.cid=c.cid
group by c.cid,c.cname,ct.targets

5. What is drill across through report?

​6. How to implement type 2 SCD using SSIS and queries?
​​

4

1. I have opened a nested transaction inside an outer transaction, if i do rollback which transaction will be undone?

2. How do you know the total transaction count?

3. I have created a table variable can we use it in a nested stored procedure? If not what is the scope of a table variable?

4. If suppose we have a user defined data type. If we can modify the length of the data type does it effects in all places across the database?

5. Can we fire a trigger manually?

6. What are the magic tables? Do we have “Updated” magic table?

7. What is the difference between UnionAll and Merge?

8. What is Copy Column transformation?

9. I have a requirement that task2 has to be executed irrespective of Task1 result. How can you accomplish this?

10. Basic difference between stored procedure and user defined function?

11. See we have a simple query that’s calling a static function, like “Select * from employee where joiningdate < getstaticdate()”? Does it call function for every time or only for matched rows? How you tune this query?

12. Can we call Dataflow as a container?

13. While using SQL configurations, how you let your package direct to choose the package configuration file?

14. Do you use a single package or multiple packages for all environments?

15. Your dataflow is configured to use event handlers. I wanted one of the transformation inside the dataflow should skip the

16. What are the latest features in SSIS 2012?

17. How to use configurations in SSIS?

18. How to validate data in SSIS? Give some example.

5

1. How to keep header in all pages – SSRS?
2. How to add custom code to change the colour of a node in report – SSRS
3. I have some .csv files, how to load them into SQL Server explain step by step.
4. How to send a report as an attachment to an email and HTML report should not be added.
5. What is the difference between OLEDB – Provider , ADO.NET and SQL Server destination?

6
​

​​1. What is a hash join in execution plan?

​2. What is a sub report?

3. Difference between drill through and sub reports?

3.​What is a shared dataset?

4. Can we use shared dataset with the subreport?
5. What is the deployment mechanism for ​​SSRS deployment?

6. What are the common performance issues in SSRS?
​7. ​Can you tell me top 5 new features in SSIS and SSRS ​Both in 2008 and 2012?​

7
​​​

1. What kind of dashboards you have prepared using SSRS reports?

​2. Have you ever tried logging in SSIS? What are the tables on which log information stored? Can we enable logging for only selected items from SSIS package? if yes how?
3. Design a package to load .xlsx files from a folder. File names must include either “Finance_” or “Local_” and load files only from the last week.

​​4. How to capture column name and row number when something failed in dataflow?
5. Design a SSIS package to load a list of excel files. Once a file is loaded that file should be moved / archived to new location.
​6. Write a query to retrieve all employee hierarchy in an organization?
7. Design a SSRS report that can support dynamic columns.

8. Why should we use CTE?

9. How to use partition tables?

10. What is ETL, why specially SSIS?

11. What’s the max parallel value to SSIS?

12. See I have written a recursive CTE, it’s been running infinitely and failed with an error. The requirement is that the recursion required for 45000 times. How could you be able to handle the situation?

8

​Q. SSIS 2008 uses all available RAM, and after package completes Memory is not released. Have you ever faced these issues if yes can you explain how you resolved it?

​Q. Can you give some examples for de-generated dimension?

Q. We have a requirement like this. For every 10 days there is a data load happens in our database using a SSIS package. My requirement is once the ETL finished successfully then a SSRS report has to be emailed to the corresponding group of members. How can you do that?

Q. How to remove PDF from the export options in SSRS report?

Q. What are the different approaches to deploying SSIS packages in development, staging and production environments?

Q. Did you remember any error codes which are occurred while executing SSIS package?

Q. I have executed an SSIS package, usually it takes 3 hours but this time the package has taken 7 hours and the execution is still in progress. Can you describe what all the various approaches to troubleshoot this issue?

9

​

1. Do you know about BI Symantec Model (BISM)?

2. Have you experienced filter index partitions
3.What is the difference between sub query and correlated query
4. What is the difference between pessimistic locking and optimistic locking?
5. What are the user roles available in SSRS?
​6. Can you write a query to find nth highest salary of an employee?

7. Write a query to delete duplicate records from a table. Note: Write queries that suits the below situation. A table is having a unique key and having duplicates records, table is not having a unique and having duplicate records.

8. What is XACT_ABORT ON?
9. How to filter nested stored procedure code from profiler?

10. How to find the number of transactions in the current scope?

11. What happens when a rollback happens in inside a nested stored procedure?
12. Example for degenerated dimension?

13. What is a bitmap index?
​14. How to avoid bookmark lookup in execution plan?
​15. ​How to avoid sort operation in SSIS?

16. ​When index scan happens?

17. What are the data regions in SSRS?

10

​1. What kind of join happens in lookup transformation?

2. Did you find any issues using Full cache mode?

3. Does temp tables and table variables both stored in tempdb?

4. Why cursors are so costly?

5. Have you ever used custom assembles in SSRS?

6. How to enhance SSRS functionality?

7. Can we move sql server logins and users using SSIS?

8. Which is the most critical ETL task you implemented using SSIS?

​11

1. Can we call a procedure from a function?

2. Can we write DML inside a function?

3. How to design a report to show the alternative rows in a different colour?

4. Write a code to customize the SSRS report. Where the code has to be written?

5. In a SSRS report where to write custom code?

​6. How to troubleshoot SSRS report using ExecutionLog2?

7. Have you ever seen .rdl file? What are the different sections in .rdl file?

​

12

​1. What is the best value for MAXDOP value?

2. Which is better “Left Outer” Or “NOT EXIST”? Explain.

3. How to find the statistics are outdated?

4. How to find the query running on a given SPID?

5. What is XACT_ABORT ON?

6. Can we use two CTE’s in a single select query?

7. What are the different join operators in SQL Server?

8. Can we use a table variable inside a nested stored procedure if the table variable created in parent stored procedure?

9. What are the limitations on “SET ROWCOUNT”?

10. While creating a “Include” columns on which basis we should consider main column and include columns?

11. How to find the last statistics update date?

13

1. An indexed view is referring only one base table. Both view and table are having index defined on them. Which index would be utilized when a query executed against the table.

2. I have an indexed view, now base table data has been modified, does the modified data reflected in view automatically?

3. Does “TRUNCATE” DDL or DML command?

4. I have written a recursive CTE, it’s been running infinitely and failed with an error. The requirement is that the recursion required for 45000 times. How could you be able to handle the situation?

​14

1. What is index reorganization?

​2. How sql engine knows which index has to be used while dealing with indexed views?

3. How to prevent bad parameter sniffing? What exactly it means?
4. What dll file that handle the transaction logs in logshipping?

5. How to find all dependent objects of a table?
6. How to find the latency in replication?

7. What are the tracer tokens in replication?
8. How to remove articles with generating a new snapshot?

9. I am not able to select some of the articles from publishing list, what might be the reason?

10. ​What is DAC? How it exactly works?

11. On which port DAC runs on?​

12. ​Which agent will take care of database mirroring?​

15

1. Why can’t we take a backup of a database which is in standby or in recovery mode?
2. How to move a database which is acting as a publisher in transactional replication?
3. What is CROSS APPLY?
4. How to find and remove duplicates from a table which is having 10 million rows?
5. Which is better a CTE or a subquery? Why?
6. Can you tell me replication monitoring tables?
7. How to apply service packs on Active Active cluster?
8. Best practices in applying security patches
9. What is a log reader agent?
10. What is PULL and PUSH subscriptions?

16

1. How to rebuild a master database? Ho to restore a master database?
2. Any alternative to triggers?
3. What are the counters to monitor CPU usage?
4. Top 5 performance tuning tools
5. What events need to be added to capture execution plan in sql profiller?
6. How to add memory to sql server 2005?
7. Which locks are held at the time of snapshot in log shipping?
8. What is the new lock escalation in sql 2008?
9. How to check the log file location for service pack 4 in sql server 2005?
10. What is a filtered index?

​17

​1. On which basis merge replication works on?
​​2. How to give a user to run a sql agent job?​

3. Can we install SQL Server using a configure file?

4. What are the top performance counters to be monitor in Performance Monitor?

5. How do you know how much memory has been allocated to sql server using AWE?

​18

​

1. What happens when a transaction runs on SQL server? Let’s say simple update statement “Update Table set col1 = value where col2 = value”
​​Ans:

​It issues an update lock and upgrades it to Exclusive Lock

The corresponding page would be captured from disk to memory

The modified page will be modified at Memory

The operation “Update *******” will be written to LDF.
Check point happens and the modified page will be written back to Disk and the operation at LDF marked as committed.

Lazy writer is responsible for cleaning the committed transactions from LDF.

2. What is fragmentation? How it happens?

3.  See we have a full backup on Sunday 8 PM, Diff and every day : 8 PM and log bkp on every 15 min. DB Crashed on Saturday afternoon 2:55 PM. How to rebuild the database? If suppose the last Sunday full backup is corrupted then how can you restore the database in current in time?

4. I have an instance on which there are databases in both FULL and SIMPLE recovery models. If I restart the sql service, what is the difference between these databases in recovering or what happens while restarting the services?

5. I have a log file which is of 250 GB. Log is full. We don’t have a disk space on any other drive for creating .ndf, auto growth is ON, and essentially there are no options to allocate new space for the file. What’s your action plan?

6. Can we do replication with mirroring? If yes what are the limitations?

7. Can we perform a tail log backup if .mdf file is corrupted?

8. Task manager is not showing the correct memory usage by SQL Server. How to identify the exact memory usage from SQL Server?

9. What is the option”Lock Pages in Memory”?

10. How to apply service pack on Active / Passive cluster on 2008 and 2012?

11. Can we configure log shipping in replicated database?

12. How to configure replication on cross domain instances?

13. Let’s say we have a situation. We are restoring a database from a full backup. The restore operation ran for 2 hours and failed with an error 9002 (Insufficient logspace). And the database went to suspect mode. How do you troubleshoot this issue?

14. Consider a situation where publisher database log file has been increasing and there there is just few MB available on disk. As an experienced professional how do you react to this situation? Remember no disk space available and also we can’t create a new log file on other drive

15. Can we add an article to the existing publication without generating a snapshot with all articles?

19

1. Difference between 32 bit and 64 bit

2. How B-Tree formed for Clustered and non clustered indexes?

3. How B-Tree forms for indexes with included column?

4. Does alzebrizer tree stores in memory for stored procedures, views and constraints?

5. What is WOW and WOW64?

6. How to design TempDB files? And what is the limit?

7. What are the different queues of CPU?

8. Write a query to show what’s happening on instance with description?

9. How VLF’s created for tempDB?

10. When the checkpoint can happen? What it exactly do?

11. When the lazywriter happens and what it’ll do?
12. What is total server memory and target server memory?

13. What is memory grant in SQL Server?

14. Why resourceDB introduced?

15. How to move master database?

16. How to rebuild master database and what are the considerations?

17. What is a boot page?

18. What is fragmentation?
19. What is edition limitation in sql server 2008 for database mirroring with asynchronous mode?

20. Do you know why SQL Browser is?

21. How to upgrade SSRS reports?
22. How do you know that log shipping break down?

23. What is the difference between push and pull subscription?

20

1. Can we truncate a table which is participating in transactional replication?

2. How to identify log filling issue and can we issue shrink with truncate on publisher database?

3. How to filter the nested stored procedure or a command from profiler?

4. Can we add articles to the existing publication without initialization of the snapshot?

5. How MAXDOP impacts SQL Server?

6. How distributed transactions works in SQL Server?

7. Full back up size is 300 GB, usually my diff backup size varies between 300 MB and 5 GB, one day unfortunately diff backup size was increased to 250 GB? What might be the reason any idea?

8. What is .TUF file? What is the significance of the same? Any implications if the file is deleted?

21

1. ​Are tables locked during generating the snapshot?
2. Does Truncate Works in replication? What are the limitations of Truncate command?
​​3. ​​Causes for slow replication?

4. How to add articles to existing publication without generating a full snapshot?
5. Can we add only new articles to merger publication?

6. What is re-initialization in replication and how it works?
​7. What is the difference between lazy writer and checkpoint?
8. How to move master database?
9. What are the different shrink options?
10. Can you explain the log file architecture?

​22

1. What is the main difference between mirroring and always on?

2. What is Microsoft Best Practices Analyzer?

3. What is Microsoft Baseline Configuration Analyzer?

4. What are the different database patterns?

5. Any idea types of data warehouse?

6. What is SCD type – 2?

7. What is the difference between “Natural Key” and “Surrogate Key”?

8. What is a junk dimension? Give me an example

9. What is a Degenerate Dimension / Fact Dimension in SQL Server Analysis Services? In what scenarios do you use it?

 ​23

1. ​​What the issues you find in migrating databases
2. ​​What is the schedule frequency of your transactional replication?
​​​3. How do check the application compatibility with sql server?​

4. ​How do you know whether statistics are latest or expired?​

5. ​​How to run distributed transactions in sql server?  What are the config changes has to be made?

6. How to give linked server usage permissions to specified logins only?

7. What kind of information that SQL Server keeps in memory?

8. Customer asked to break the mirroring and failover to mirror database. What are the steps to be taken other than a manual failover?

9. Can you give some examples for One to One, One to Many and Many to Many relationships?

​24

​1. How to find the tempdb contention?

2. What is the sparse file?

3. What is the redo file in log shipping?

4. What are the queues in sql server?

5. How to capture a trace from production without any impact on performance?

6. How to capture the long running queries?

7. What is the migration plan to move 300 databases to  a new data centre? We can have an hour downtime.

8. In mirroring a connection failure happened between principal and mirror and principal server started filling log space (send queue), how do you troubleshoot?

9. What are the phases a database needs to be gone through while restoring?

10. What is the recovery interval?

11. You have any idea on Table Partitions?

​25

1. ​We have a log shipping environment. New data file has been added at primary server, what happens and how do you resolve it?

2. See we have a view which is getting data from different tables. One day it’s starts executing infinitely. I have seen no blocking, no bulk operation happened. I have stopped all jobs and maintenance plans on the server. No one is connected to the database but still it’s been taking longer time. What might be the possible reasons?

3. You have got a request to execute a query which is an “Update” query. That update is updating 5 million rows, after an hour it’s still executing and you are getting lot of requests from report users that their things are getting slow down. What’s your action plan?

4. See I have an environment, Sunday night full backup, everyday night diff backup and every 45 min a transactional backup. Disaster happened at 2:30 PM on Saturday. You suddenly found that the last Sunday backup has been corrupted. What’s your recovery plan?

5. Full backup size is 300 GB, usually my diff backup size varies between 300 MB and 5 GB, one day unfortunately diff backup size was increased to 250 GB? What might be the reason any idea?

6. What is .TUF file? What is the significance of the same? Any implications if the file is deleted?

7. What are the ITIL basic standards? What are all the phases of ITIL? Explain about incident management, problem management, change management etc?

8. Can you explain sql server transaction log architecture?

9. What are the phases of sql server database restore process?​

​​26

1. How many IP’s required configuring a 2 node cluster?

2. How many MSDTC required for a 2 node cluster?

3. What is the basic difference between 2005 and 2008 in clustering?

4. What’s the use of quorum in clustering?

5. Your customer complained that one of the reports is not working, what is your action plan? Note: You just know the database server not anything else about that report.

6. How could you give full access on a database to a user from “Operations-Team”. Remember the user should have all rights except write permission. But our company policy is not to give DB_OWNER rights to any user from “Operations-Team”

​​7. I wanted to know what are the maximum worker threads setting and active worker thread count on sql server. Can you tell me how to capture this info? What’s the default value for max thread count?

8. What are the all possibilities that cause the tempdb full issue?

9. What is version store?

10. What is the best configuration for Tempdb?

11. We have a procedure which is running fine till today afternoon. Suddenly it started taking long time to execute and there of it leads to a timeout error from application. What might be happening? How you troubleshoot?

12. Do you have any idea about sparse column?

13. Have you ever done any automation in your database environment?

14. What are the critical issues you faced in your career?

15. Did you ever handle any missed SLA’s?

16. How to change the port number for SQL Server?

17. Any idea about capacity planning?

27

1. How to give estimations to your report requirements?

2. Difference between ISNULL and COAELSCE

3. What is the tough SSIS package you handled?

4. What is the difference between BCP and Bulk insert?
5. On which basis we can give the deadline for a given task?

6. I have a requirement: We need to load a bunch of files on every Thursday at 4:00 AM EST and once the load is completed successfully a pre designed SSRS report has to be triggered and it has to be mailed to the given recipients. Design a ETL package using SSIS

28

1. Write a query to capture all employee details with salary less than the average salary within each department.

2. I have a table employee in that I have a column empID which is of varchar type. The column may have combination of characters and integers. Now write a query to get all records in which empID are having integers. Exclude rows with EMPID is not having integer values in it.

3. We are doing a ETL operations using stored procedures. Write a procedure to cleansing data in staging table and insert the data into master tables. Remember in staging table all columns are of varchar type

4. What is database unit testing? How to perform unit test for a stored procedure and SSIS package?

5. Assume we need to design a SSIS package to load data from a .csv file to database. In .csv file there are 10 columns. For the first 500 rows data is available for all 10 columns and for the last 400 rows data is available for first 6 columns, not even comma available after 6th column. How do you handle this?

.csv file:

col1, col2, col3, col4, col5

‘dat’, ‘dat’, ‘dat’, ‘dat’, ‘dat’,
‘dat’, ‘dat’, ‘dat’, ‘dat’, ‘dat’,
‘dat’, ‘dat’, ‘dat’, ‘dat’, ‘dat’,
‘dat’, ‘dat’, ‘dat’
‘dat’, ‘dat’, ‘dat’
‘dat’, ‘dat’, ‘dat’

6. What are the different types of storage models in OLAP?

7. What is a mini dimension?

8. Design a SSRS report that can support dynamic columns.

9. How to remove PDF option from export options in SSRS report?

10. How to design a SSRS report that shows alternative rows in different colour?

29

1. What is connection pooling in sql server?

2. Difference between partition by and patindex

3. What are the database design patterns?

4. What are the storage models in OLAP?

5. What is the difference between CROSS / OUTER APPLY AND JOINS in T-SQL?

6. When to use CROSS APPLY over Join?

7. Do you have any idea about table partitions?

8. How to attach configuration files to SSIS package?

9. What is stuff function? Difference between stuff and replace?

10. What is sparse column?

11. We have a query which is running fine in development but facing performance issues at production. You got the execution plan from production DBA. Now you need to compare with the development execution plan. What is your approach?

12. How to manually allocate memory to SSRS service?

13. How to view report server logs and call stacks in SSRS?

14. We know in SSRS by default datasets are executed in parallel. But in our environment datasource is under high load and can’t handle parallel requests. Now can you explain how to disable parallel processing or how to serialize dataset execution?

15. How to pass multi-valued parameter to stored procedure in dataset?

16. How to control the pagination in SSRS?

17. What are the major differences between SSRS 2008 and SSRS 2012?

18. You have any idea about IIF, SWITCH and LOOKUP functions in SSRS?

19. How to get “Total” values at the end of every group in a report?

20. A SSIS package failed how to know the exact row number at which the package failed to process?

The post Interview Questions appeared first on udayarumilli.com.

SQL Server Security – Interview questions with answers

1. What is the Guest user account in SQL Server?  What login is it mapped to it?  

Ans:

The Guest user account is created by default in all databases and is used when explicit permissions are not granted to access an object.  It is not mapped directly to any login, but can be used by any login.  Depending on your security needs, it may make sense to drop the Guest user account, in all databases except Master and TempDB

2. What is the use of BUILTIN\Administrators Group in SQL Server?

Ans:

Any Windows login in BUILTIN\Administrators group is by default a SQL Server system administrator. This single group can be used to manage administrators from a Windows and SQL Server perspective

3. We have a list of 3 SQL Server logins which are dedicated to a critical application. We have given all required rights to those logins. Now my question is we have to restrict the access only to these three logins. Means there are two conditions:

a) No other user should be able to access the database except those three logins

b) Even for those three logins they should be able to run their queries only through the application. If someone login through SSMS and trying to run a query should result into a failure.

Finally there should be only way to running a query is from their application using one of those three logins, there should be no other way to run queries on that database. How do you restrict?

Ans:

• Do not give access to any other login on that database except for those 3 app logins.
• Create a trigger that test each and every query like below

IF app_name() in(‘SQL Query Analyzer’,’Microsoft SQL Server Management Studio’)
raiserror (…..)
Return

4. How to resolve the orphan use problem?

Ans:

Such a user is said to be an orphaned user of the database on that server instance. A database user can become orphaned if the corresponding SQL Server login is dropped. Also, a database user can become orphaned after a database is restored or attached to a different instance of SQL Server. Orphaning can happen if the database user is mapped to a SID that is not present in the new server instance.

• To find out the orphan users

USE <database_name>;

GO;

sp_change_users_login @Action='Report';

GO;

• To resolve the orphan user problem

USE <database_name>;

GO

sp_change_users_login @Action='update_one', 
@UserNamePattern='<database_user>',

@LoginName='<login_name>';

GO

5. What are the fixed server level roles?

Ans:

• SysAdmin – Can perform any activity
• ServerAdmin – Can change server configuration, restart, shutdown server
• SecurityAdmin – Can manage server level logins, also can manage db level if they have permission on db
• Granted: ALTER ANY LOGIN
• ProcessAdmin – Can kill a process on an instance
• Granted: ALTER ANY CONNECTION, ALTER SERVER STATE
• DiskAdmin – Can manage the disk files
• Granted: ALTER RESOURCES
• BulkAdmin – Can perform BULK INSERT
• Granted: ADMINISTER BULK OPERATIONS
• SetupAdmin – Can add and remove linked servers
• Granted: ALTER ANY LINKED SERVER
• Dbcreator – Can create, alter, drop and restore any database on the instance
• Granted: CREATE ANY DATABASE
• Public – Default role for newly created login

sp_helpsrvrolemember : List out the members mapped with the server roles

6. What are the Database roles?

Ans:

• db_accessadmin – Granted: ALTER ANY USER, CREATE SCHEMA, Granted with Grant option – Connect
• db_backupoperator – Granted: BACKUP DATABASE, BACKUP LOG, CHECKPOINT
• db_datareader – Granted – SELECT
• db_datawriter – Granted – INSERT, UPDATE and DELETE
• db_ddladmin – Granted – Any DDL operation
• db_denydatareader – Denied – SELECT
• db_denydatawriter – Denied – INSERT, UPDATE and DELETE
• db_owner – Granted with GRANT option: CONTROL
• db_securityadmin – Granted: ALTER ANY APPLICATION ROLE, ALTER ANY ROLE, CREATE SCHEMA, VIEW DEFINITION
• dbm_monitor – Granted: VIEW most recent status in Database Mirroring Monitor

sp_helprolemember : List out the members mapped with the server roles

Note:

Fixed database roles are not equivalent to their database-level permission. For example, the db_owner fixed database role has the CONTROL DATABASE permission. But granting the CONTROL DATABASE permission does not make a user a member of the db_owner fixed database role.

7. What are the security related catalog views?

Where the security related information stored on?

Ans:

• Server Level:
• Sys.server_permissions
• Sys.server_principals
• Sys.server_role_members
• Sys.sql_logins

• Database Level:
• Sys.database_permissions
• Sys.database_principals
• Sys.database_role_members

8. What are the extra roles available in msdb?

Ans:

• db_ssisadmin: Equals to sysadmin
• db_ssisoperator: Import/Delete/Change Role of own packages
• db_ssisltduser: Only can view and execute the packages
• dc_admin : Can administrate and use the data collector
• dc_operator: Can administrate and use the data collector
• dc_proxy : Can administrate and use the data collector
• PolicyAdministratorRole: can perform all configuration and maintenance activities on Policy-Based Management policies and conditions.
• ServerGroupAdministratorRole : Can administrate the registered server group
• ServerGroupReaderRole: Can view and the registered server group
• dbm_monitor: Created in the msdb database when the first database is registered in Database Mirroring Monitor

9. If you lose rights to your SQL Server instance what are the options to connect to SQL SERVER Instance?

Ans:

Option1: Use the Dedicated Administrator Connection

Option2: Use BUILTIN\Administrators Group

Option3: Change Registry Values

10. What objects does the fn_my_permissions function reports on?

Ans:

• SERVER
• DATABASE
• SCHEMA
• OBJECT
• USER
• LOGIN
• ROLE
• APPLICATION ROLE
• TYPE
• MESSAGE TYPE
• ASYMMETRIC KEY
• SYMMETRIC KEY
• CERTIFICATE
• SERVICE
• REMOTE SERVICE BINDING
• FULLTEXT CATALOG
• ASSEMBLY
• CONTRACT
• ENDPOINT
• ROUTE
• XML SCHEMA COLLECTION

SELECT * FROM fn_my_permissions(NULL, ‘SERVER’);

SELECT * FROM fn_my_permissions(‘AdventureWorks’, ‘DATABASE’);

SELECT * FROM fn_my_permissions(‘Employee’, ‘OBJECT’)

11. Name three of the features managed by the Surface Area Configuration tool.

Ans:

• Ad-hoc remote queries
• Common language runtime
• Dedicated Administrator Connection
• Database Mail
• Native XML Web Services
• OLE Automation
• Service Broker
• SQL Mail
• Web Assistant
• xp_cmdshell

12. What options are available to audit login activity?

Ans:

• Custom solution with your application to log all logins into a centralized table
• Enable login auditing at the instance level in Management Studio
• Execute Profiler to capture logins into the instance
• Leverage a third party product

13. How to perform backup for Certificates in sql server?

Ans:

• Using Native Backup
• Using Backup Certificate Command

14. Name 3 of the features that the SQL Server built-in function LOGINPROPERTY performs on standard logins.

Ans:

• Date when the password was set
• Locked out standard login
• Expired password
• Must change password at next login
• Count of consecutive failed login attempts
• Time of the last failed login attempt
• Amount of time since the password policy has been applied to the login
• Date when the login was locked out
• Password hash

15. How can SQL Server instances be hidden?

Ans:

To hide a SQL Server instance, we need to make a change in SQL Server Configuration Manager. To do this launch SQL Server Configuration Manager and do the following: select the instance of SQL Server, right click and select Properties. After selecting properties you will just set Hide Instance to “Yes” and click OK or Apply. After the change is made, you need to restart the instance of SQL Server to not expose the name of the instance.

16. Is Profiler the only tool that has the ability to audit and identify DDL events?

Ans:

No. In SQL Server 2005 DDL triggers were introduced to audit CREATE, ALTER and DROP events for relational (stored procedures, functions, views, etc.) and security (certificates, logins, server, etc.) objects.

17. What are some of the pros and cons of not dropping the SQL Server BUILTIN\Administrators Group?

Ans:

Pros:

• Any Windows login is by default a SQL Server system administrator
• This single group can be used to manage SQL Server from a system administrators perspective

Cons:

• Any Windows login is by default a SQL Server system administrator, which may not be a desired situation

18. What is SQL Injection and why is it a problem?

Ans:

SQL Injection is an exploit where unhandled\unexpected SQL commands are passed to SQL Server in a malicious manner.  It is a problem because unknowingly data can be stolen, deleted, updated, inserted or corrupted.

19. How can SQL Injection be stopped?

Ans:

Development\DBA

• Validate the SQL commands that are being passed by the front end
• Validate the length and data type per parameter
• Convert dynamic SQL to stored procedures with parameters
• Prevent any commands from executing with the combination of or all of the following commands: semi-colon, EXEC, CAST, SET, two dashes, apostrophe, etc.
• Based on your front end programming language determine what special characters should be removed before any commands are passed to SQL Server

Network Administration

• Prevent traffic from particular IP addresses or domains
• Review the firewall settings to determine if SQL Injection attacks can prevented
• Remove old web pages and directories that are no longer in use because these can be crawled and exploited
• Research products or services to scan your code and web site on a regular basis to prevent the issue
  • http://www.acunetix.com/vulnerability-scanner/
  • http://www.rapid7.com/nexpose/web-application-va.jsp
  • http://www.fortify.com/products/detect/
  • http://www.mcafeesecure.com/us/
  • http://www.onlinehackscan.com/default.asp

20. How to recover from SQL Injection?

Ans:

If for some reason the resolution implemented does not resolve the problem and the SQL Injection attack occurs again, the quickest path may be to do the following:

• Shut down the web sites
• Review the IIS logs to determine the commands issued and which web page\command has the vulnerability
• Convert the code to determine which tables were affected and the command issued
• Find and replace the string in your tables
• Correct the web page\command that has the vulnerability
• Test to validate the issue no longer occurs
• Deploy the web page\command
• Re-enable the web sites

21. How to enforce Security in SQL SERVER?

Ans:

By providing strong Passwords, Limited the access to make sure right people have access to the right data, Creating Customized database roles, server roles and assign privileges and by choosing the correct authentication mode etc.

A DBA should be careful in providing security…..General precautions includes:

• Minimize the number of sysadmins allowed to access SQL Server.
• Give users the least amount of permissions they need to perform their job.
• Use stored procedures or views to allow users to access data instead of letting them directly access tables.
• When possible, use Windows Authentication logins instead of SQL Server logins.
• Don’t grant permissions to the public database role.
• Remove user login IDs who no longer need access to SQL Server.
• Avoid creating network shares on any SQL Server.
• Turn on login auditing so you can see who has succeeded, and failed, to login.
• Ensure that your SQL Servers are behind a firewall and are not exposed directly to the Internet.
• Using server, database and application roles to control access to the data
• Securing the physical database files using NTFS permissions
• Using an un guessable SA password
• Restricting physical access to the SQL Server
• Disabling the Guest account
• Isolating SQL Server from the web server
• Choose either of the service to run SQL Server (Local User – Not an Admin , Domain User – Not an Admin)
• Restrict the remote administration (TC)
• If SQL Server authentication is used, the credentials are secured over the network by using IPSec or SSL, or by installing a database server certificate.
• Do not use DBO users as application logins
• Firewall restrictions ensure that only the SQL Server listening port is available on the database server.
• Remove the SQL guest user account.
• Remove the BUILTIN\Administrators server login.
• Apply the latest security updates / patches

We have plenty of features in SQL SERVER to enforce the security. The major features include:

• Password policies
• Encryption
• Limited metadata visibility (system Tables to Catalog Views)
• DDL triggers
• User-schema separation
• Impersonation
• Granular permission sets
• Security catalog views

In addition to these features we have some more added in SQL SERVER 2008, like Policy Based Management, Security Audit, Improved Encryption, Backup Security etc.

When we talk about the security we have to consider the bellow

• Patches and Updates
• Services
• Protocols
• Accounts
• Files and Directories
• Shares
• Ports
• Registry
• Auditing and Logging
• SQL Server Security
• SQL Server Logins, Users, and Roles
• SQL Server Database Objects

22. You are delegating permissions on your SQL Server 2005 server to other administrators. You have local, single server jobs on one server that you would like to allow another administer to start, stop, and view the history for, but not delete history. This administrator will own the jobs. Which role should you assign?

Ans:

SQLAgentUserRole
SQL Server 2005 provides 3 fixed roles for the agent service that limit privileges for administrators. The SQLAgentUserRole is designed for local jobs (not multiserver) that allow the member to work with their owned jobs (edit, start, stop, view history) without deleting the history of any job.

The post MSSQL Security – Interview Questions and Answers appeared first on udayarumilli.com.

Concurrency Control And Locking

Concurrency and Locking – Interview Questions with answers

1. What are the concurrent problems occur in accessing database?

Ans:

Tr – Transaction

R – Resource

Uncommitted dependency/dirty reads:

Tr1 Updates Data R1

Tr2 Reads Data R1

Tr1 Rollback the Update Operation R1

Now Tr2 has the inconsistent data or wrong data.

Inconsistent Analysis/non-repeatable reads

Tr1 Reads Data R1

Tr2 Updates Data R1

Tr1 Again Reads the same data R1

Wrong match between first Tr1 and Second time Tr1

Phantom reads (via insert/delete)

Tr1 Reads Data (Result Contains 10 Records R1

Tr2 Insert/Delete Data (insert 6 new delete 1 Record) R1

Tr1 Again reads the same data R1

In Second time Tr1 we found 6 New Records and we can’t find a record which retrieves in first time…..

2. What isolation levels will provide completely read-consistent views of a database to all transactions?

Ans:

SQL Server 2000: Only the SERIALIZABLE isolation level will provide a completely read-consistent view of a database to a given transaction. In any of the other isolation levels, you could perceive some/all of the following, depending on the isolation level running in:

• • Uncommitted dependency/dirty reads
  • Inconsistent Analysis/non-repeatable reads
  • Phantom reads (via insert/delete)

SQL Server 2005 and above: Both the SERIALIZABLE and SNAPSHOT isolation levels will provide a completely read-consistent view of a database to a given transaction. In any of the other isolation levels, you could perceive some/all of the following, depending on the isolation level running in:

• • Uncommitted dependency/dirty reads
  • Inconsistent Analysis/non-repeatable reads
  • Phantom reads (via insert/delete)

3. Within the READ_COMMITTED isolation level, during a read operation how long are locks held/retained for?

Ans:

When SQL Server executes a statement at the read committed isolation level, it acquires short lived share locks on a row by row basis. The duration of these share locks is just long enough to read and process each row; the server generally releases each lock before proceeding to the next row. Thus, if you run a simple select statement under read committed and check for locks, you will typically see at most a single row lock at a time. The sole purpose of these locks is to ensure that the statement only reads and returns committed data. The locks work because updates always acquire an exclusive lock which blocks any readers trying to acquire a share lock.

4. Within the REPEATABLE_READ and SERIALIZABLE isolation levels, during a read operation and assuming row-level locking, how long are locks held/retained for?

Ans:

Within either of these isolation levels, locks are held for the duration of the transaction, unlike within the READ_COMMITTED isolation level as noted above.

5. Can locks ever be de-escalated?

Ans:

No, locks are only escalated, never de-escalated.

6. What are the different types of lock modes in SQL Server?

Ans:

• Shared
• Update
• Exclusive
• Schema (modification and stability)
• Bulk Update
• Intent (shared, update, exclusive)
• Key Range (shared, insert, exclusive)

7. Can you explain scenarios where each type of lock would be taken?

Ans:

SHARED: Used for read operations that do not change or update data, such as a SELECT statement.

UPDATE: Update locks (U) are acquired just prior to modifying the data. If a transaction modifies a row, then the update lock is escalated to an exclusive lock; otherwise, it is converted to a shared lock. Only one transaction can acquire update locks to a resource at one time. Using update locks prevents multiple connections from having a shared lock that want to eventually modify a resource using an exclusive lock. Shared locks are compatible with other shared locks, but are not compatible with Update locks.

EXCLUSIVE: Used for data-modification operations, such as INSERT, UPDATE, or DELETE. Ensures that multiple updates cannot be made to the same resource at the same time.

INTENT: Used to establish a lock hierarchy. The types of intent locks are: intent shared (IS), intent exclusive (IX), and shared with intent exclusive (SIX). (Another question in the Difficult level section expands on this)

SCHEMA: Used when an operation dependent on the schema of a table is executing. The types of schema locks are: schema modification (Sch-M) and schema stability (Sch-S).

BULK UPDATE: Used when bulk copying data into a table and the TABLOCK hint is specified.

KEY RANGE: Protects the range of rows read by a query when using the serializable transaction isolation level. Ensures that other transactions cannot insert rows that would qualify for the queries of the serializable transaction if the queries were run again.

8. What is lock escalation and what triggers it?

Ans:

The process of converting many fine-grained locks into fewer coarse-grained locks is known as Lock Escalation.

** Escalation reduces system resource consumption/overhead while increasing the possibility of concurrency conflicts

**To escalate locks, the Database Engine attempts to change the intent lock on the table to the corresponding full lock, for example, changing an intent exclusive (IX) lock to an exclusive (X) lock, or an intent shared (IS) lock to a shared (S) lock). If the lock escalation attempt succeeds and the full table lock is acquired, then all heap or B-tree, page (PAGE), key-range (KEY), or row-level (RID) locks held by the transaction on the heap or index are released. If the full lock cannot be acquired, no lock escalation happens at that time and the Database Engine will continue to acquire row, key, or page locks.

**Lock escalation is triggered at either of these times:

• When a single Transact-SQL statement acquires at least 5,000 locks on a single table or index.
• When the number of locks in an instance of the Database Engine exceeds memory or configuration thresholds.
• If locks cannot be escalated because of lock conflicts, the Database Engine periodically triggers lock escalation at every 1,250 new locks acquired.

9. Name as many of the lockable resources as possible in SQL Server?

Ans:

• RID (single row on a heap)
• KEY (single row (or range) on an index)
• PAGE
• EXTENT
• HOBT (heap or b-tree)
• TABLE (entire table, all data and indexes)
• FILE
• APPLICATION
• METADATA
• ALLOCATION_UNIT
• DATABASE

10. What requirements must be met for a BULK-UPDATE lock to be granted, and what benefit do they server?

Ans:

The Database Engine uses bulk update (BU) locks when bulk copying data into a table, and either the TABLOCK hint is specified or the table lock on bulk load table option is set using sp_tableoption. Bulk update (BU) locks allow multiple threads to bulk load data concurrently into the same table while preventing other processes that are not bulk loading data from accessing the table.

11. What is the least restrictive type of lock? What is the most restrictive?

Ans:

The least restrictive type of lock is a shared lock. The most restrictive type of lock is a schema-modification

12. What is a deadlock and how is it different from a standard block situation?

Ans:

A deadlock occurs when two or more tasks permanently block each other by each task having a lock on a resource which the other tasks are trying to lock. In a deadlock situation, both transactions in the deadlock will wait forever unless the deadlock is broken by an external process – in a standard blocking scenario, the blocked task will simply wait until the blocking task releases the conflicting lock scenario.

13. Which 2 isolation levels support optimistic/row-versioned-based concurrency control?

Ans:

First is the READ COMMITTED isolation level.  This is the only level that supports both a pessimistic (locking-based) and optimistic (version-based) concurrency control model. Second is SNAPSHOT isolation level that supports only an optimistic concurrency control model.

14. What database options must be set to allow the use of optimistic models?

Ans:

READ_COMMITTED_SNAPSHOT option for the read committed optimistic model. ALLOW_SNAPSHOT_ISOLATION option for the snapshot isolation level

15. What is the size of a lock structure?

Ans: 

96 bytes

16. In what circumstances will you see key-range locks, and what are they meant to protect against?

Ans:

You will only see key-range locks when operating in the SERIALIZABLE isolation level.

• Key-range locks protect a range of rows implicitly included in a record set being read by a Transact-SQL statement. The serializable isolation level requires that any query executed during a transaction must obtain the same set of rows every time it is executed during the transaction. A key range lock protects this requirement by preventing other transactions from inserting new rows whose keys would fall in the range of keys read by the serializable transaction.
• Key-range locking prevents phantom reads. By protecting the ranges of keys between rows, it also prevents phantom insertions into a set of records accessed by a transaction.

17. Explain the purpose of INTENT locks?

Ans:

The Database Engine uses intent locks to protect placing a shared (S) lock or exclusive (X) lock on a resource lower in the lock hierarchy. Intent locks are named intent locks because they are acquired before a lock at the lower level, and therefore signal intent to place locks at a lower level. Intent locks serve two purposes:

• To prevent other transactions from modifying the higher-level resource in a way that would invalidate the lock at the lower level.
• To improve the efficiency of the Database Engine in detecting lock conflicts at the higher level of granularity.

18. Can deadlocks occur on resources other than database object?

Ans:

YES.

19. What are the different types of resources that can deadlock?

Ans:

Deadlock is a condition that can occur on any system with multiple threads, not just on a relational database management system, and can occur for resources other than locks on database objects. Here are the resources:

Locks – Waiting to acquire locks on resources, such as objects, pages, rows, metadata, and applications can cause deadlock.

Worker threads – A queued task waiting for an available worker thread can cause deadlock. If the queued task owns resources that are blocking all worker threads, a deadlock will result

Memory – When concurrent requests are waiting for memory grants that cannot be satisfied with the available memory, a deadlock can occur.

Parallel query execution-related resources – Coordinator, producer, or consumer threads associated with an exchange port may block each other causing a deadlock usually when including at least one other process that is not a part of the parallel query. Also, when a parallel query starts execution, SQL Server determines the degree of parallelism, or the number of worker threads, based upon the current workload. If the system workload unexpectedly changes, for example, where new queries start running on the server or the system runs out of worker threads, then a deadlock could occur.

Multiple Active Result Sets (MARS) resources – Resources used to control interleaving of multiple active requests under MARS, including:

• User resource – when a thread is waiting for a resource that is potentially controlled by a user application, the resource is considered to be an external or user resource and is treated like a lock
• Session mutex – The tasks running in one session are interleaved, meaning that only one task can run under the session at a given time. Before the task can run, it must have exclusive access to the session mutex.
• Transaction mutex – All tasks running in one transaction are interleaved, meaning that only one task can run under the transaction at a given time. Before the task can run, it must have exclusive access to the transaction mutex.

20. Explain how the database engine manages the memory footprint for the lock pool when running in a dynamic lock management mode.

Ans

SQL Server 2000: When the server is started with locks set to 0, the lock manager allocates two percent of the memory allocated to SQL Server to an initial pool of lock structures. As the pool of locks is exhausted, additional locks are allocated. The dynamic lock pool does not allocate more than 40 percent of the memory allocated to SQL Server.

• Generally, if more memory is required for locks than is available in current memory, and more server memory is available (the max server memory threshold has not been reached), SQL Server allocates memory dynamically to satisfy the request for locks. However, if allocating that memory would cause paging at the operating system level (for example, if another application was running on the same computer as an instance of SQL Server and using that memory), more lock space is not allocated.

SQL Server 2005: When running in dynamic management mode (i.e. if the server is started with locks configuration option set to 0), the lock manager acquires sufficient memory from the Database Engine for an initial pool of 2,500 lock structures. As the lock pool is exhausted, additional memory is acquired for the pool.

• Generally, if more memory is required for the lock pool than is available in the Database Engine memory pool, and more computer memory is available (the max server memory threshold has not been reached), the Database Engine allocates memory dynamically to satisfy the request for locks. However, if allocating that memory would cause paging at the operating system level (for example, if another application is running on the same computer as an instance of SQL Server and using that memory), more lock space is not allocated. The dynamic lock pool does not acquire more than 60 percent of the memory allocated to the Database Engine. After the lock pool has reached 60 percent of the memory acquired by an instance of the Database Engine, or no more memory is available on the computer, further requests for locks generate an error.

21. Describe the differences between the pessimistic SERIALIZABLE model and the optimistic SNAPSHOT model in terms of transactional isolation (i.e., not the concurrency differences, but instead how the exact same transactional modifications may result in different final outcomes).

Ans:

• It is typically relatively simple to understand SERIALIZABLE. For the outcome of two transactions to be considered SERIALIZABLE, it must be possible to achieve this outcome by running one transaction at a time in some order.
• Snapshot does not guarantee this level of transactional isolation.
• Imagine the following sample scenario:

Serializable:

There is a bag containing a mixture of white and black marbles. Suppose that we want to run two transactions. One transaction turns each of the white marbles into black marbles. The second transaction turns each of the black marbles into white marbles. If we run these transactions under SERIALIZABLE isolation, we must run them one at a time. The first transaction will leave a bag with marbles of only one color. After that, the second transaction will change all of these marbles to the other color. There are only two possible outcomes: a bag with only white marbles or a bag with only black marbles.

Snapshot:

If we run these transactions under snapshot isolation, there is a third outcome that is not possible under SERIALIZABLE isolation. Each transaction can simultaneously take a snapshot of the bag of marbles as it exists before we make any changes. Now one transaction finds the white marbles and turns them into black marbles. At the same time, the other transactions finds the black marbles – but only those marbles that where black when we took the snapshot – not those marbles that the first transaction changed to black – and turns them into white marbles. In the end, we still have a mixed bag of marbles with some white and some black. In fact, we have precisely switched each marble.

22. What are the different isolation levels available?

Ans:

• Read Uncommitted Isolation Level
• Read Committed Isolation Level
• Repeatable Read Isolation Level
• Serializable Isolation Level
• Snapshot Isolation Level
• Read Committed Snapshot Isolation Level

23. Demonstrate Isolation levels?

Ans:

• Read Uncommitted: This is the lowest isolation level. It only isolates transactions and activities to ensure that physically corrupt data is never read. It allows dirty reads, nonrepeatable reads, and phantom reads.
• Read Committed: This isolation level does not permit dirty reads, but does allow nonrepeatable reads and phantom reads. This is the default isolation level for SQL Server, and is used for each connection to SQL Server unless one of the other isolation levels has manually been set for a connection.
• Repeatable Read: This isolation level does not permit dirty reads or nonrepeatable reads, but does allow phantom reads.
• Serializable Read: This is the highest isolation level and ensures that all transactions and statements are completely isolated from each other. It does not allow dirty reads, nonrepeatable reads, or phantom reads.

New isolation levels that introduced in SQL 2005 based on row versioning:

• READ_COMMITTED_SNAPSHOT (statement level): READ_COMMITTED_SNAPSHOT is actually a variation of the default READ_COMMITTED isolation level. It uses row versioning, instead of locking, to provide read consistency at the SQL Server statement level. When a statement runs that specifies the READ_COMMITTED isolation level (the default isolation level), and the READ_COMMITTED_SNAPSHOT option is turned on at the database level, all statements see a snapshot of the data as it existed at the start of any current transaction. It uses the row-versioned snapshot of the row to return data, and no locking is needed by the statement, which is normally the case. The biggest benefit of this isolation level is that reads do not block writes and writes do not block reads. Writes can still block writes, but this is necessary to prevent data corruption.
• ALLOW_SNAPSHOT_ISOLATION (transaction level): ALLOW_SNAPSHOT_ISOLATION is similar to READ_COMMITTED_SNAPSHOT, but it is based at the transaction level, not the statement level. When the ALLOW_SNAPSHOT_ISOLATION is turned on at the database level and the TRANSACTION ISOLATION LEVEL SNAPSHOT isolation level is turned on for the transaction (using the SET command), all statements see a snapshot of the data as it existed at the start of the transaction.

24. Any idea about row versioning?

Ans:

The concept of row versioning is not new to SQL Server, as SQL Server has been using it for years with triggers. For example, when a DELETE trigger is executed for a row, a copy of that row is stored in the “deleted table” just in case the trigger is rolled back and the deleted row needs to be “undeleted.” In a sense, the row is versioned, and if need be, can be reused.

Row versioning for isolation levels is very similar, though not identical to row versioning for triggers. When a row versioning-based isolation level (which includes the two new ones we are now discussing) is enabled at the database level, the database engine maintains versions of each row that is modified (for an entire database). Whenever a transaction modifies any row, an image of the row before the modification is copied into a page of what is called the version store. The version store is located in the tempdb database and is used for temporary storage of versioned rows for all of the databases on a single SQL Server instance.

25. What are the properties of a transaction?

Ans:

There are 4 properties called ACID.

Atomicity: All changes to data are performed as if they are a single operation. That is, all the changes are performed, or none of them are.

Example: In an application that transfers funds from one account to another, the atomicity property ensures that, if a debit is made successfully from one account, the corresponding credit is made to the other account.

Consistency: Data is in a consistent state when a transaction starts and when it ends.

Example: In an application that transfers funds from one account to another, the consistency property ensures that the total value of funds in both the accounts is the same at the start and end of each transaction.

Isolation: The intermediate state of a transaction is invisible to other transactions. As a result, transactions that run concurrently appear to be serialized.

Example: in an application that transfers funds from one account to another, the isolation property ensures that another transaction sees the transferred funds in one account or the other, but not in both, nor in neither.

Durability: After a transaction successfully completes, changes to data persist and are not undone, even in the event of a system failure.

Example: in an application that transfers funds from one account to another, the durability property ensures that the changes made to each account will not be reversed.

26. How to find out and prevent Deadlocks?

Ans:

To find Deadlocks

Error:

Transaction (Process ID 52) was deadlocked on lock resources with another process and has been chosen as the deadlock victim. Rerun the transaction.

There are two popular ways to identifying the deadlocks

• Enabling a Trace Flag
• By default Deadlocks are not written into sql server errorlog, to do so we have to enable a trace flag.
• Trace Flag 1204 – SQL Server 2000 or below
• Trace Flag 1222 – SQL Server 2005 or above
• Syntax: DBCC TRACEON (1222, -1)

Note: -1 indicates trace should run for all sessions

• Using the profiler:
• We need to capture the Lock Events Lock: Deadlock and Lock: Deadlock Chain along with the ObjectID data column

To prevent Deadlocks:

• While updating have the application access server objects in the same order each time.
• During transactions, don’t allow any user input. Collect it before the transaction begins.
• Keep transactions as short as possible. To accomplish this when your application does need to read the same data more than once, cache it by storing it in a variable or an array, and then re-reading it from there, not from SQL Server.
• Reduce lock time. Develop your application to grab locks at the latest possible time, and then releases them at the very earliest time.
• If appropriate, reduce lock escalation by using the ROWLOCK or PAGLOCK.
• Consider using the NOLOCK hint to prevent locking if the data being locked is not modified often.
• If appropriate, use low level isolation level according to the possibilities
• Look for other opportunities to improve the efficiency of the queries
• If both deadlock participants are using the same index, consider adding an index that can provide an alternate access path to one of the spids.

Thanks

The post MSSQL Concurrency Control and Locking – MSSQL Interview questions with answers appeared first on udayarumilli.com.

SQL DBA Interview Questions and Answers – 1

SQL Server Database Administrator – Interview Questions

Q. What is the maximum limit of SQL Server instances for a standalone computer? (2008 R2)

Ans:

50 instances on a stand-alone server for all SQL Server editions. SQL Server supports 25 instances on a failover cluster.

Q. What is the cluster node limitation?

Ans:

The number of allowable nodes in the SQL Server cluster depends on your SQL Server version and your Windows Server version. For SQL Server 2008 Standard edition, you can only have two cluster nodes. If you have SQL Server Enterprise, the limit depends on your Windows Server version, 8 cluster nodes for 2003 and 16 nodes for 2008.

Q. Can we install SQL Server using a configure file?

Ans:

Yes! We can prepare a configuration file. While installing SQL Server the path to the configuration file is specified in the “Ready to Install” page in the configuration file path section. Cancel the setup without actually completing the installation, to generate the INI file.

File Location and Name:

%programfiles%\Microsoft SQL Server\110\Setup Bootstrap\Log\<YYYYMMDD_HHMM>\ConfigurationFile.ini.

Q. How to install a SQL Server using configuration file?

Ans:

From Command prompt locate the setup.exe file location and can install using config file.

Setup.exe /ConfigurationFile=MyConfigurationFile.INI

Instead of specifying passwords inside the config file specify them explicitly as below.

Setup.exe /SQLSVCPASSWORD=”************” /AGTSVCPASSWORD=”************” /ASSVCPASSWORD=”************” /ISSVCPASSWORD=”************” /RSSVCPASSWORD=”************” /ConfigurationFile=MyConfigurationFile.INI

Q. What are the top performance counters to be monitor in Performance Monitor?

Ans:

Processor\%Processor Time: Monitoring CPU consumption allows you to check for a bottleneck on the server (indicated by high sustained usage).

High percentage of Signal Wait: Signal wait is the time a worker spends waiting for CPU time after it has finished waiting on something else (such as a lock, a latch or some other wait). Time spent waiting on the CPU is indicative of a CPU bottleneck. Signal wait can be found by executing DBCC SQLPERF (waitstats) on SQL Server 2000 or by querying sys.dm_os_wait_stats on SQL Server 2005.

Physical Disk\Avg. Disk Queue Length: Check for disk bottlenecks: if the value exceeds 2 then it is likely that a disk bottleneck exists.

MSSQL$Instance: Buffer Manager\Page Life Expectancy: Page Life Expectancy is the number of seconds a page stays in the buffer cache. A low number indicates that pages are being evicted without spending much time in the cache, which reduces the effectiveness of the cache.

MSSQL$Instance: Plan Cache\Cache Hit Ratio: A low Plan Cache hit ratio means that plans are not being reused.

MSSQL$Instance:General Statistics\Processes Blocked: Long blocks indicate contention for resources.

Q. Task manager is not showing the correct memory usage by SQL Server. How to identify the exact memory usage from SQL Server?

Ans:

To know the exact memory usage relay on column “physical_memory_in_use_kb” from DMV “sys.dm_os_process_memory”.

Using performance counters also we can find the usage.

Performance object: Process

Counter: Private Bytes

Instance: sqlservr

Performance object: Process

Counter: Working Set

Instance: sqlservr

The Private Bytes counter measures the memory that is currently committed. The Working Set counter measures the physical memory that is currently occupied by the process.

For 64-bit sql servers we can also check the current memory usage using the below performance counter.

Performance object: SQL Server:Memory Manager

Counter: Total Server Memory (KB)

Q. What is the option ”Lock Pages in Memory”?

Ans:

Lock Pages in Memory is a setting that can be set on 64-bit operating systems that essentially tell Windows not to swap out SQL Server memory to disk. By default, this setting is turned off on 64-bit systems, but depends on various conditions this option needs to be turned on.

We must be very careful in dealing with this option. One can enable this after a detailed analysis of current environment.

Following issues may rise when “Lock Pages in Memory” is not turned on:

• SQL Server performance suddenly decreases.
• Application that connects to SQL Server may encounter timeouts.
• The hardware running SQL Server may not respond for a short time periods.

Q. How do you know how much memory has been allocated to sql server using AWE?

Ans:

We can use DBCC MEMORYSTSTUS command to know the memory allocation information. But it’s trick to understand the results.

We can use a DMV called “sys.DM_OS_Memory_Clerks”. Sample query to calculate total AWE memory allocated is “SELECT SUM(awe_allocated_kb) FROM sys.dm_os_memory_clerks”

From 2008 onwards we can get all memory related information using DMV “sys.dm_os_process_memory”.

Q. How to apply service pack on Active / Passive cluster on 2008 and 2012?

Ans:

1. Freeze the service groups on Node A (active node).

2. Confirm all SQL services are stopped on Node B.

3. Upgrade the SQL Server 2008 instance on Node B.

4. Reboot node B.

5. Unfreeze the service group on node A.

6. Fail over the service group to Node B.

7. After the service group comes online, freeze the service group on Node B.

8. Confirm all SQL services are stopped on Node A.

9. Upgrade the SQL Server 2008 instance on Node A.

10. Reboot Node A.

11. Unfreeze the service group on node B.

12. Fail back the service group to Node A.

Q. How to apply a SP on SQL Server 2005 Active / Passive cluster?

Ans:

1. Login to the Console on the target node

a. RDP to the console is ok, but a standard RDP connection is not recommended.

2. Copy the Service Pack to a local drive on the target node

3. Move all instances to the target node

a. You can only install on the Active Node.

4. Move the Cluster Resource to the target node

5. Move the MSDTC Resource to the target node

6. Verify all users are logged out from all other nodes (RDP and Console sessions)

7. Start the Service Pack install

a. Use a domain account with admin rights to all servers.

b. Ignore locked files

8. Reboot current server

a. You should not need to perform the install on any other nodes, nor reboot them. The service pack will update the passive nodes first.

Q. You find SP is not applied on all the nodes across the cluster. How to apply SP only on required nodes?

Ans:

If you find that the product level is not consistent across all the nodes, you will need to fool the 2005 patch installer into only patching the nodes that need updating. To do so, you will have to perform the following steps:

1. Fail Instance, Cluster, and MSDTC groups to an unpatched node
2. Remove any successfully patched nodes from failover candidates of the SQL Server Service of the instance group (do this using Cluster Admin tool)
3. Run the patch
4. After the patch installs successfully, add the Nodes removed in Step 2 back to the SQL Server Service of the Instance group

Why do you need to do this? Well when the patch installer determines that not all nodes in the cluster are at the same patch level, a passive node operation will fail and will prevent you from moving forward with any further patching.

Q. How to change the sql server service account in a cluster environment?

Ans:

Method 1: (No failover required)

1. Freeze the service group on active node from cluster administrator and then restart the service.

Method2:

1. Offline the SQL resources

2. Update the service account at SSCM and restart the service as needed

3. Add the SQL resources back to online

Note: Don’t forget to update service account at the remaining nodes on the cluster.

Method 3:

1. Node 2 (inactive node) change the SQL startup account in SQL Studio or SCM

2. Fail over the SQL service group from node 1 to node 2.

3. Node 1 (now the inactive node) change the SQL startup account in SQL Studio or SCM

Q. How to apply service pack on Active / Active cluster Nodes?

Ans:

1. Make a note of all node names (and/or IP addresses), SQL Server virtual names along with preferred nodes. If there are more than three nodes you may need to also take note of possible owners for each SQL resource group. For my example assume that I have a cluster with node1 and node2, SQL1 normally lives on node1 and SQL2 normally lives on node2.

2. To start with a clean slate and ensure any previous updates are completed both nodes should be restarted if possible. Choose the physical node that you you want to patch second and restart that node (in my example node2).

3. Restart the node you want to patch first (node1). This will mean that both active SQL instances are now running on node2. Some restarts will be essential, but you could avoid the first two restarts if you need to keep downtime to a minimum and just fail SQL1 over to node2. The main point here is to always patch a passive node.

4. In cluster administrator remove node1 from the possible owners lists of SQL1 and SQL2. This means that neither SQL instance can fail over to node1 while it is being patched.

5. Run the service pack executable on node1.

6. Restart node1.

7. Add node1 back into the possible owners lists of SQL1 and SQL2 and fail both instances over to node1.

8. Repeat steps 4 – 6 on node2.

9. Add node2 back into the possible owners lists of SQL1 and SQL2 and fail both instances over to node2. Check that the build level is correct and review the SQL Server error logs.

10. Fail SQL1 over to node1. Check build levels and SQL Server error logs

Q. What are the main events and columns helpful in troubleshooting performance issues using profiler?

Ans:

Events:

Event Group: Performance

Event: ShowPlan_ALL (BinaryData column must be selected)

Event: ShowPlan_XML

Event Group: T-SQL

Event: SQL:BatchStarted

Event: SQL:BatchCompleted

Event Group: Stored Procedures

Event: RPC:Completed

Event Group: Locks

Event: Lock: Deadlock Graph

Event: Lock: Lock Deadlock Chain (Series of events that leaads to a deadlock)

Event Group: Sessions

Event: Existing Connection

Event Group: Security Audit

Event: Audit Login

Event: Audit Log Out

Columns:

Below are the most common columns that help us in understanding the trace file to troubleshoot the problems.

TextData

ApplicationName

NTUserName

LoginName

CPU

Reads

Writes

Duration

SPID

StartTime

EndTime

Database Name

Error

HostName

LinkedServerName

NTDomainName

ServerName

SQLHandle

All these columns need not be available for all of the events, but depends on the event select we have to choose the appropriate columns.

Filters:

ApplicationName

DatabaseName

DBUserName

Error

HostName

NTUserName

NTDomainName

Q. What are the agents in replication?

Ans:

Snapshot Agent: Copy Schema+Data to snapshot folder on distributer. Used in all types of replication.

Log reader Agent: Sends transactions from Publisher to Distributor. Used in transactional replication

Distribution Agent: Applies Snapshots / Transactions to all subscribers’ runs at distributer in PUSH and Runs at Subscriber in PULL. Used in transactional and transactional with updatable subscriptions.

Queue reader Agent: Runs at distributer send back transactions from subscriber to publisher. Used in Transactional With updatable subscriptions.

Merge Agent: Applies initial snapshot to subscribers, from the next time synchronize by resolving

the conflicts.

Q. Can we configure log shipping in replicated database?

Ans: Yes

Replication does not continue after a log shipping failover. If a failover occurs, replication agents do not connect to the secondary, so transactions are not replicated to Subscribers. If a failback to the primary occurs, replication resumes. All transactions that log shipping copies from the secondary back to the primary are replicated to Subscribers.

For transactional replication, the behavior of log shipping depends on the sync with backup option. This option can be set on the publication database and distribution database; in log shipping for the Publisher, only the setting on the publication database is relevant.

Setting this option on the publication database ensures that transactions are not delivered to the distribution database until they are backed up at the publication database. The last publication database backup can then be restored at the secondary server without any possibility of the distribution database having transactions that the restored publication database does not have. This option guarantees that if the Publisher fails over to a secondary server, consistency is maintained between the Publisher, Distributor, and Subscribers. Latency and throughput are affected because transactions cannot be delivered to the distribution database until they have been backed up at the Publisher.

Q. What are the best RAID levels to use with SQL Server?

Ans:

Before choosing the RAID (Redundant Array of Independent Disks) we should have a look into usage of SQL Server files.

As a basic thumb rule “Data Files” need random access, “Log files” need sequential access and “TempDB” must be on a fastest drive and must be separated from data and log files.

We have to consider the below factors while choosing the RAID level:

Reliability

Storage Efficiency

Random Read

Random Write

Sequential Write

Sequential Write

Cost.

As an Admin we have to consider all of these parameters in choosing the proper RAID level. Obviously the choice is always between RAID-5 and RAID-10

Q. How to monitor latency in replication?

Ans:

There are three methods.

1. Replication monitor
2. Replication commands
3. Tracer Tokens

1. Replication Monitor: In replication monitor from the list of all subscriptions just double click on the desired subscription. There we find three tabs.

• Publisher to Distributor History
• Distributor to Subscriber History
• Undistributed commands

2. Replication Commands:

Publisher.SP_ReplTran: Checks the pending transactions at p

Distributor.MSReplCommands and MSReplTransactions: Gives the transactions and commands details. Actual T_SQL data is in binary format. From the entry time we can estimate the latency.

Distributor.SP_BrowseReplCmds: It shows the eaxct_seqno along with the corresponding T-SQL command

sp_replmonitorsubscriptionpendingcmds: It shows the total number of pending commands to be applied at subscriber along with the estimated time.

3. Tracer Tokens:

Available from Replication Monitor or via TSQL statements, Tracer Tokens are special timestamp transactions written to the Publisher’s Transaction Log and picked up by the Log Reader. They are then read by the Distribution Agent and written to the Subscriber. Timestamps for each step are recorded in tracking tables in the Distribution Database and can be displayed in Replication Monitor or via TSQL statements.

When Log Reader picks up Token it records time in MStracer_tokens table in the Distribution database. The Distribution Agent then picks up the Token and records Subscriber(s) write time in the MStracer_history tables also in the Distribution database.

Below is the T-SQL code to use Tracer tokens to troubleshoot the latency issues.

–A SQL Agent JOB to insert a new Tracer Token in the publication database.

USE [AdventureWorks]

Go

EXEC sys.sp_posttracertoken @publication = <PublicationName>

Go

–Token Tracking Tables

USE Distribution

Go

–publisher_commit

SELECT Top 20 * FROM MStracer_tokens Order by tracer_id desc

–subscriber_commit

SELECT Top 20 * FROM MStracer_history Order by parent_tracer_id desc

Q. Can we perform a tail log backup if .mdf file is corrupted?

Ans:

Yes we can perform a tail log as long as the ldf if not corrupted and no bulk logged changes.

A typical tail log backup is having two options, 1. WITH NORECOVERY 2.Continue After Error.

1. WITH NORECOVERY: To make sure no transactions happens after the tal log backup

2. CONTINUE AFTER ERROR: Just to make sure log backup happens even though some meta data pages corrupted.

Q. Let’s say we have a situation. We are restoring a database from a full backup. The restore operation ran for 2 hours and failed with an error 9002 (Insufficient logspace). And the database went to suspect mode. How do you troubleshoot this issue?

Ans:

In that case we can actually add a new log file on other drive and rerun the restore operation using the system stored procedure “sp_add_log_file_recover_suspect_db”. Parameters are the same as while creating a new log file.

Q. Let’s say we have a situation. We are restoring a database from a full backup. The restores operation runs for 2 hours and failed with an error 1105 (Insufficient space on the file group). And the database went to suspect mode. How do you troubleshoot this issue?

Ans:

In that case we can actually add a new data file on another drive and rerun the restore operation using the system stored procedure “sp_add_data_file_recover_suspect_db”. Parameters are the same as while creating a new data file.

Q. Can you describe factors that causes the logfile grow?

Ans:

• CHECKPOINT has not occurred since last log truncation
• No log backup happens since last full backup when database is in full recovery
• An active BACKUP or RESTORE operation is running from long back
• Long running active transactions
• Database mirroring is paused or mode is in high performance
• In replication publisher transactions are not yet delivered to distributer
• Huge number of database snapshots is being created

Q. How do you troubleshoot a Full transaction log issue?

Ans:

Columns log_reuse_wait and log_reuse_wait_desc of the sys.databases catalog view describes what is the actual problem that causes log full / delay truncation.

• Backing up the log.
• Freeing disk space so that the log can automatically grow.
• Moving the log file to a disk drive with sufficient space.
• Increasing the size of a log file.
• Adding a log file on a different disk.
• Completing or killing a long-running transaction.

http://msdn.microsoft.com/en-us/library/ms345414.aspx

Q. Does “Truncate” works in transactional replication?

Ans:

No! As per MSDN blogs information we can’t use TRUNCATE on published database against the published article instead we have to use “DELETE” without where clause.

Q. Consider a situation where publisher database log file has been increasing and there there is just few MB available on disk. As an experienced professional how do you react to this situation? Remember no disk space available and also we can’t create a new log file on other drive

Ans:

Essentially we have to identify the bottleneck which is filling the log file.

As a quick resolution check all possible solutions as below:

• Resolve if there are any errors in log reader agent / distribution agent
• Fix if there are any connectivity issues either between publisher – distributor or distributor
• Fix if there are any issues with I/O at any level
• Check if there is any huge number of transactions pending from publisher
• Check if there are any large number of VLF’s (USE DBCC Loginfo)which slows the logreader agent work.
• Check all database statistics are up-to-date at distributer. Usually we do siwtch off this “Auto Update Stats” by default.
• To find and resolve these issues we can use “Replication Monitor”, “DBCC Commands”, “SQL Profiler”, “System Tables / SP / Function”.

If incase we can’t resolve just by providing a simple solution we have to shrink the transaction log file. Below are two methods.

To shrink the transaction log file:

1. Backup the log — So transactions in vlf’s are marked as inactive

2. Shrink the logfile using DBCC SHRINKFILE – Inactive VLF’s would be removed

3. If you find no difference in size repeat the above steps 1 and 2

To truncate the transaction log file:

In any case we are not able to provide the solution against the increasing logfile the final solution is disable the replication, truncate the log and reinitialize the subscribers.

1. Disable replication jobs

2. Execute SP_ReplDone procedure. It disable the replication and mark as “Replicate done” for all pending transactions at publisher.

3. Backup the transaction log “WITH TRUNCATE” option.

4. Shrink the log file using “DBCC SHRINKFILE”

5. Flues the article cache using “sp_replflush”.

6. Go to distributor database and truncate the table MSRepl_Commands

7. Connect to replication monitor and reinitialize all subscriptions by generating a new snapshot.

8. Enable all replication related jobs.

Q. Can we add an article to the existing publication without generating a snapshot with all articles?

Ans:

Yes! We can do that. Follow the below steps to publish a new article to the existing publication.

There are two parameters that we need to change to “False”. 1. Immediate Sync and 2. Allow_Ananymous.

Both the fields were set to ON by default. If the Immediate_sync is enabled every time you add a new article it will cause the entire snapshot to be applied and not the one for the particular article alone.

Steps:

1. Change the values to “True” for publication properties “Immediate_Sync” and “Allow_Anonymous” using SP_CHANGEPUBLICATION

2. Add a new article to the publication using SP_AddArticle. While executing this procedure along with the required parameters also specify the parameter “@force_invalidate_snapshot=1”.

3. Add the subscriptions to the publication for the single table/article uisng “SP_ADDSUBSCRIPTION”. While executing this proc specify the parameter “@Reserved = Internal”. Generate a new snapshot which only includes newly added article.

Q. How MAXDOP impacts SQL Server?

Ans:

The Microsoft SQL Server max degree of parallelism (MAXDOP) configuration option controls the number of processors that are used for the execution of a query in a parallel plan. This option determines the computing and threads resources that are used for the query plan operators that perform the work in parallel.

For servers that use more than eight processors, use the following configuration:

MAXDOP=8

For servers that use eight or fewer processors, use the following configuration:

MAXDOP=0 to N

Q. How distributed transactions works in SQL Server?

Ans:

Distributed transactions are the transactions that worked across the databases, instances in the given session. Snapshot isolation level does not support distributed transactions.

We can explicitly start a distributed transaction using “BEGIN DISTRIBUTED TRANSACTION <TranName>”

For example, if BEGIN DISTRIBUTED TRANSACTION is issued on ServerA, the session calls a stored procedure on ServerB and another stored procedure on ServerC. The stored procedure on ServerC executes a distributed query against ServerD, and then all four computers are involved in the distributed transaction. The instance of the Database Engine on ServerA is the originating controlling instance for the transaction.

When a distributed query is executed in a local transaction, the transaction is automatically promoted to a distributed transaction if the target OLE DB data source supports ITransactionLocal. If the target OLE DB data source does not support ITransactionLocal, only read-only operations are allowed in the distributed query.

In order to work with these transactions, make sure below settings are done.

1. MSDTC must be running on all supported instances

2. Choose the option “No authentigation required” from MSDTC properties

3. Turn on random options at linked server properties like “RPC”, “RPC Out”, “Data Access” etc.

Q. Can you give some examples for One to One, One to Many and Many to Many relationships?

Ans:

One to One: Citizen – UID

A citizen can have only one UID – A UID can represent only one citizen

One to Many: Customer – Products

A customer can sale number of products – A product can be brought by only one customer

​Many to Many: ​Book – Author

​A book can be written by more than one author – An author can write more than one book​

Q. What are the phases of sql server database restore process?​

​Ans:

​1. Copy Data: Copies all data,log and index pages from backup file to database mdf, ndf and ldf files

​ 2. REDO: Rollfoward all committed transactions to database and if it finds any uncommitted transactions it goes to the final phase UNDO.

3. UNDO: Rollback any uncommitted transactions and make database available to users.

Q. I wanted to know what are the maximum worker threads setting and active worker thread count on sql server. Can you tell me how to capture this info? What’s the default value for max thread count?

Ans:

We can check the current settings and thread allocation using the below queries.

–Thread setting

select max_workers_count from sys.dm_os_sys_info

–Active threads

select count(*) from sys.dm_os_threads

Default value is 255.

Increasing the number of worker threads may actually decrease the performance because too many threads causes context switching which could take so much of the resources that the OS starts to degrade in overall performance.

Q. Can you explain sql server transaction log architecture?

Ans:

​We need to spend some time on this as every SQL DBA must aware of this concept.

http://www.sqlservercentral.com/articles/Stairway+Series/73775/

Q. See I have an environment, Sunday night full backup, everyday night diff backup and every 45 min a transactional backup. Disaster happened at 2:30 PM on Saturday. You suddenly found that the last Sunday backup has been corrupted. What’s your recovery plan?

Ans:

​When you find that the last full backup is corrupted or otherwise unrestorable, making all differentials after that point useless. You then need to go back a further week to the previous full backup (taken 13 days ago), and restore that, plus the differential from 8 days ago, and the subsequent 8 days of transaction logs (assuming none of those ended up corrupted!).

If you’re taking daily full backups, a corrupted full backup only introduce an additional 24 hours of logs to restore.

Alternatively, a log shipped copy of the database could save your bacon (you have a warm standby, and you know the log backups are definitely good).

​

Q. Full backup size is 300 GB, usually my diff backup size varies between 300 MB and 5 GB, one day unfortunately diff backup size was increased to 250 GB? What might be the reason any idea?

Ans:

Are you the kind of DBA who rebuilds all indexes nightly? Your differential backups can easily be nearly as large as your full backup. That means you’re taking up nearly twice the space just to store the backups, and even worse, you’re talking about twice the time to restore the database.

To avoid these issues with diff backups , ideally schedule the index maintenance to happen right before the full backup.

Q. What is .TUF file? What is the significance of the same? Any implications if the file is deleted?

Ans:

.TUF file is the Transaction Undo File, which is created when performing log shipping to a server in Standby mode.

When the database is in Standby mode the database recovery is done when the log is restored; and this mode also creates a file on destination server with .TUF extension which is the transaction undo file.

This file contains information on all the modifications performed at the time backup is taken.

The file plays a important role in Standby mode… the reason being very obvious while restoring the log backup all uncommited transactions are recorded to the undo file with only commited transactions written to disk which enables the users to read the database. So when we restore next transaction log backup; SQL server will fetch all the uncommited transactions from undo file and check with the new transaction log backup whether commited or not.

If found to be commited the transactions will be written to disk else it will be stored in undo file until it gets commited or rolledback.

​If .tuf file is got deleted there is no way to repair logshipping except reconfiguring it from scratch.

​

The post SQL DBA – INTERVIEW QUESTIONS WITH ANSWERS – 1 appeared first on udayarumilli.com.

SQL DBA Interview Questions and Answers – 2

SQL Server Database Administrator – Interview Questions

Q. Can we hot add CPU to sql server?

Ans:

Yes! Adding CPUs can occur physically by adding new hardware, logically by online hardware partitioning, or virtually through a virtualization layer. Starting with SQL Server 2008, SQL Server supports hot add CPU.

• Requires hardware that supports hot add CPU.
• Requires the 64-bit edition of Windows Server 2008 Datacenter or the Windows Server 2008 Enterprise Edition for Itanium-Based Systems operating system.
• Requires SQL Server Enterprise.
• SQL Server cannot be configured to use soft NUMA

Once the CPU is added just run RECONFIGURE then sql server recognizes the newly added CPU.

Q: How can we check whether the port number is connecting or not on a Server?

Ans:

TELNET <HOSTNAME> PORTNUMBER

TELNET PAXT3DEVSQL24 1433

TELNET PAXT3DEVSQL24 1434

Common Ports:

MSSQL Server: 1433

HTTP TCP 80

HTTPS TCP 443

Q: What is the port numbers used for SQL Server services?

Ans:

• The default SQL Server port is 1433 but only if it’s a default install. Named instances get a random port number.
• The browser service runs on port UDP 1434.
• Reporting services is a web service – so it’s port 80, or 443 if it’s SSL enabled.
• Analysis service is on 2382 but only if it’s a default install. Named instances get a random port number.

Q: Start SQL Server in different modes?

Ans:

Single User Mode (-m) : sqlcmd –m –d master –S PAXT3DEVSQL11 –c –U sa –P *******

DAC (-A): sqlcmd –A –d master –S PAXT3DEVSQL11 –c –U sa –P *******

Emergency: ALTER DATABASE test_db SET EMERGENCY

Q: How to recover a database that is in suspect stage?

Ans:

ALTER DATABASE test_db SET EMERGENCY

After you execute this statement SQL Server will shutdown the database and restart it without recovering it. This will allow you to view / query database objects, but the database will be in read-only mode. Any attempt to modify data will result in an error similar to the following:

Msg 3908, Level 16, State 1, Line 1 Could not run BEGIN TRANSACTION in database ‘test’ …..etc

ALTER DATABASE test SET SINGLE_USER

GO

DBCC CHECKDB (‘test’, REPAIR_ALLOW_DATA_LOSS) GO

If DBCC CHECKDB statement above succeeds the database is brought back online (but you’ll have to place it in multi-user mode before your users can connect to it). Before you turn the database over to your users you should run other statements to ensure its transactional consistency. If DBCC CHECKDB fails then there is no way to repair the database – you must restore it from a backup.

Q. Can we uninstall/rollback a service packs from SQL Server 2005?

Ans:

No not possible for SQL Server 2005. To rollback a SP you have to uninstall entire product and reinstall it.

For Sql Server 2008 you can uninstall a SP from Add/Remove programs.

Some people are saying that we can do it by backup and replace the resource db. But I am not sure about that.

Q. What is a deadlock and what is a live lock? How will you go about resolving deadlocks?

Ans:

Deadlock is a situation when two processes, each having a lock on one piece of data, attempt to acquire a lock on the other’s piece. Each process would wait indefinitely for the other to release the lock, unless one of the user processes is terminated. SQL Server detects deadlocks and terminates one user’s process.

A livelock is one, where a request for an exclusive lock is repeatedly denied because a series of overlapping shared locks keeps interfering. SQL Server detects the situation after four denials and refuses further shared locks. A livelock also occurs when read transactions monopolize a table or page, forcing a write transaction to wait indefinitely.

Q. SQL Server is not responding. What is action plan?

Ans:

Connect using DAC via CMD or SSMS

Connect via CMD

SQLCMD -A –U myadminlogin –P mypassword -SMyServer –dmaster

Once you connect to the master database run the diagnostic quires to find the problem

Correct the issue and restart the server

Find the errors from sql log using

SQLCMD –A –SmyServer –q”Exec xp_readerrorlog” –o”C:\logout.txt”

A long running query blocking all processes and not allowing new connections

Write a query and put the script file on hard disk Ex: D:\Scripts\BlockingQuery.sql

use master;

select p.spid, t.text

from sysprocesses p

CROSS APPLY sys.dm_exec_sql_text (sql_handle) t

where p.blocked = 0

and p.spid in

( select p1.blocked

from sysprocesses p1

where p1.blocked > 0

and p1.waittime > 50 )

From command prompt run the script on sql server and get the result to a text file

SQLCMD -A – SMyServer -i”C:\SQLScripts\GetBlockers.sql” -o”C:\SQLScripts\blockers.txt”

Recently added some data files to temp db and after that SQL Server is not responding

This can occur when you specify new files in a directory to which the SQL Server service account does not have access.

Start the sql server in minimal configuration mode using the startup parameter “–f”. When we specify –f the sql server creates new tempdb files at default file locations and ignore the current tempdb data files configuration. Take care when using –f as it keep the server in single user mode.

Once the server is started change the tempdb configuration settings and restart the server in full mode by removing the flag -f

A database stays in a SUSPECT or RECOVERY_PENDING State

Try to resolve this using CheckDB and any other DBCC commands if you can.

Last and final option is put the db in emergency mode and run CHECKDB with repair_allow_data_loss

(Note: Try to avoid this unless you don’t have any option as you may lose large amounts of data)

Q. What is your experience with third party applications and why would you use them?

Ans:
I have used some of the 3^rd Party tools:

• SQL CHECK – Idera – Monitoring server activities and memory levels
• SQL DOC 2 – RedGate – Documenting the databases
• SQL Backup 5 – RedGate – Automating the Backup Process
• SQL Prompt – RedGate – Provides IntelliSense for SQL SERVER 2005/2000,
• Lite Speed 5.0 – Quest Soft – Backup and Restore

Benefits using Third Party Tools:

• Faster backups and restores
• Flexible backup and recovery options
• Secure backups with encryption
• Enterprise view of your backup and recovery environment
• Easily identify optimal backup settings
• Visibility into the transaction log and transaction log backups
• Timeline view of backup history and schedules
• Recover individual database objects
• Encapsulate a complete database restore into a single file to speed up restore time
• When we need to improve upon the functionality that SQL Server offers natively
• Save time, better information or notification

Q. Why sql server is better than other databases?

Ans:

I am not going to say one is better than other, but it depends on the requirements. We have number of products in market. But if I have the chance to choose one of them I will choose SQL SERVER because…..

• According to the 2005 Survey of Wintercorp, The largest SQL Server DW database is the 19.5 terabytes. It is a database of a European Bank
• High Security. It is offering high level of security.
• Speed and Concurrency, SQL Server 2005 system is able to handles 5,000 transactions per second and 100,000 queries a day and can scale up to 8 million new rows of data per day,
• Finally more technical peoples are available for SQL SERVER when we compare to any other database.

So that we can say SQL SERVER is more than enough for any type of application.

Q. Differences between SQL SERVER 2000 AND 2005?

Ans:

Security

• 2000: Owner = Schema, hard to remove old users at times Schema is separate.
• 2005: Better granularity in easily controlling security. Logins can be authenticated by certificates.

Encryption

• 2000: No options built in, expensive third party options with proprietary skills required to implement properly.
• 2005: Encryption and key management build in.

High Availability

• 2000: Clustering or Log Shipping requires Enterprise Edition and Expensive hardware.
• 2005: Clustering, Database Mirroring or Log Shipping available in Standard Edition. Database Mirroring can use cheap hardware.

Scalability

• 2000: Limited to 2GB, 4CPUs in Standard Edition. Limited 64-bit support
• 2005: 4 CPU, no RAM limit in Standard Edition. More 64-bit options offer chances for consolidation.

Q. What are the Hotfixes and Patches?

Ans:

Hotfixs are software patches that were applied to live i.e. still running systems. A hotfix is a single, cumulative package that includes one or more files that are used to address a problem in a software product (i.e. a software bug).

In a Microsoft SQL SERVER context, hotfixes are small patches designed to address specific issues, most commonly to freshly-discovered security holes.

Ex: If a select query returning duplicate rows with aggregations the result may be wrong….

Q. Why Shrink file/ Shrink DB/ Auto Shrink is really bad?

Ans:

In the SHRINKFILE command, SQL Server isn’t especially careful about where it puts the pages being moved from the end of the file to open pages towards the beginning of the file.

• The data becomes fragmented, potentially up to 100% fragmentation, this is a performance killer for your database;
• The operation is slow – all pointers to / from the page / rows being moved have to be fixed up, and the SHRINKFILE operation is single-threaded, so it can be really slow (the single-threaded nature of SHRINKFILE is not going to change any time soon)

Recommendations:

• Shrink the file by using Truncate Only: First it removes the inactive part of the log and then perform shrink operation
• Rebuild / Reorganize the indexes once the shrink is done so the Fragmentation level is decreased

Q. Which key provides the strongest encryption?

Ans:

AES (256 bit)

The longer the key, the better the encryption, so choose longer keys for more encryption. However there is a larger performance penalty for longer keys. DES is a relatively old and weaker algorithm than AES.

AES: Advanced Encryption Standard

DES: Data Encryption Standard

Q. What is the difference between memory and disk storage?

Ans:

Memory and disk storage both refer to internal storage space in a computer. The term “memory” usually means RAM (Random Access Memory). The terms “disk space” and “storage” usually refer to hard drive storage.

Q. What port do you need to open on your server firewall to enable named pipes connections?

Ans:
Port 445. Named pipes communicate across TCP port 445.

Q. What are the different log files and how to access it?

Ans:

• SQL Server Error Log: The Error Log, the most important log file, is used to troubleshoot system problems. SQL Server retains backups of the previous six logs, naming each archived log file sequentially. The current error log file is named ERRORLOG. To view the error log, which is located in the %Program-Files%\Microsoft SQL Server\MSSQL.1\MSSQL\LOG\ERRORLOG directory, open SSMS, expand a server node, expand Management, and click SQL Server Logs

• SQL Server Agent Log: SQL Server’s job scheduling subsystem, SQL Server Agent, maintains a set of log files with warning and error messages about the jobs it has run, written to the %ProgramFiles%\Microsoft SQL Server\MSSQL.1\MSSQL\LOG directory. SQL Server will maintain up to nine SQL Server Agent error log files. The current log file is named SQLAGENT.OUT, whereas archived files are numbered sequentially. You can view SQL Server Agent logs by using SQL Server Management Studio (SSMS). Expand a server node, expand Management, click SQL Server Logs, and select the check box for SQL Server Agent.

• Windows Event Log: An important source of information for troubleshooting SQL Server errors, the Windows Event log contains three useful logs. The application log records events in SQL Server and SQL Server Agent and can be used by SQL Server Integration Services (SSIS) packages. The security log records authentication information, and the system log records service startup and shutdown information. To view the Windows Event log, go to Administrative Tools, Event Viewer.

• SQL Server Setup Log: You might already be familiar with the SQL Server Setup log, which is located at %ProgramFiles%\Microsoft SQL Server\90\Setup Bootstrap\LOG\Summary.txt. If the summary.txt log file shows a component failure, you can investigate the root cause by looking at the component’s log, which you’ll find in the %Program-Files%\Microsoft SQL Server\90\Setup Bootstrap\LOG\Files directory.

• SQL Server Profiler Log: SQL Server Profiler, the primary application-tracing tool in SQL Server, captures the system’s current database activity and writes it to a file for later analysis. You can find the Profiler logs in the log .trc file in the %ProgramFiles%\Microsoft SQL Server\MSSQL.1\MSSQL\LOG directory.

Q. Explain XP_READERRORLOG or SP_READERRORLOG

Ans:

Xp_readerrorlog or sp_readerrorlog has 7 parameters.

Xp_readerrorlog <Log_FileNo>,<Log_Type>,<Keyword-1>,<Keyword-2>,<Date1>,<Date2>,<’Asc’/’Desc’>

Log_FileNo: -1: All logs

0: Current log file

1: No1 archived log file etc

Log_Type: 1: SQL Server

2: SQL Agent

KeyWord-1: Search for the keyword

KeyWord-2: Search for combination of Keyword 1 and Keyword 2

Date1 and Date2: Retrieves data between these two dates

‘Asc’/’Desc’: Order the data

Examples:

EXEC Xp_readerrorlog 0 – Current SQL Server log

EXEC Xp_readerrorlog 0, 1 – Current SQL Server log

EXEC Xp_readerrorlog 0, 2 – Current SQL Agent log

EXEC Xp_readerrorlog -1 – Entire log file

EXEC Xp_readerrorlog 0, 1, ’dbcc’ – Current SQL server log with dbcc in the string

EXEC Xp_readerrorlog 1, 1, ’dbcc’, ’error’ – Archived 1 SQL server log with dbcc and error in the string

EXEC xp_readerrorlog -1, 1, ‘dbcc’, ‘error’, ‘2012-02-21′, ‘2012-02-22′,’desc’

Search entire sql server log file for string ‘dbcc’ and ‘Error’ within the given dates and retrieves in descending order.

Note: Also, to increase the number of log files, add a new registry key “NumErrorLogs” (REG_DWORD) under below location.
HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\MSSQL.X\MSSQLServer\
By default, this key is absent. Modify the value to the number of logs that you want to maintain.

Q. Can we track no of transactions  / inserts / updates / deletes a Day (Without using profiler)? If yes how?

Ans:

You could use capture data change or change tracking:

http://msdn.microsoft.com/en-us/library/cc280519.aspx

Q. We have 300 SSIS packages those needs to be deployed to production, how can we make it easier / short way to deploy all SSIS packages at once.

Ans:

I would store these as XML based files and not in the MSDB database. With the configuration files, you can point the packages from prod to dev (and vice versa) in just a few seconds. The packages and config files are just stored in a directory of your choice. Resources permitting, create a standalone SSIS server away from the primary SQL Server

Q. We have a table which is 1.2 GB in size, we need to write a SP which should work with a particular point of time data (like snapshot) (We should not use snapshot Isolation as it take other 1.2 TB size)

Ans:

You may want to add insert timestamps and update timestamps for each record. Every time a new record is inserted, stamp it with the datetime, and also stamp it with the date time when updated. Also possibly use partitioning to reduce index rebuilds.

Q. What is RAID levels? Which one we have to choose for SQL Server user databases?

Ans:

Check out the charts in this document. It shows how the disks are setup. It will depend on what the customer wants to spend and level of reliability needed. Raid 5 is common, but see the topic ‘RAID 10 versus RAID 5 in Relational Databases’, in the document below. It’s a good discussion. Raid 10 (pronounced Raid one-zero) is supposed to have the best in terms of performance and reliability, but the cost is higher.

http://en.wikipedia.org/wiki/RAID

Q. How many datafiles I can put in Tempdb? What is the effect of adding multiple data files.

Ans:

By far, the most effective configuration is to set tempdb on its own separate fast drive away from the user databases. I would set the number of files based on # of cpu’s divided by 2. So, if you have 8 cpu’s, then set 4 tempdb files. Set the tempdb large enough with 10% data growth. I would start at a general size of 10 GB for each size. I also would not create more than 4 files for each mdf/ldf even if there were more than 8 cpu’s. you can always add more later.

http://msdn.microsoft.com/en-us/library/ms175527.aspx

http://msdn.microsoft.com/en-us/library/ms190768.aspx

Q. Let’s say a user is performing a transaction on a clustered server and failover has occurred. What will happen to the Transaction?

Ans:

If it is active/passive, there is a good chance the transaction died, but active/passive is considered by some the better as it is not as difficult to administer. I believe that is what we have on active. Still, active/active may be best depending on what the requirements are for the system.

Q. How you do which node is active and which is passive. What are the criteria for deciding the active node?

Ans:

Open Cluster Administrator, check the SQL Server group where you can see current owner. So current owner is the active node and other nodes are passive.

Q. What is the common trace flags used with SQL Server?

Ans:

Deadlock Information: 1204, 1205, 1222

Network Database files: 1807

Log Record for Connections: 4013

Skip Startup Stored Procedures: 4022

Disable Locking Hints: 8755

Forces uniform extent allocations instead of mixed page allocations 1118 – (SQL 2005 and 2008) To reduces TempDB contention.

Q. What is a Trace flag? Types of Trace Flags? How to enable/disable it? How to monitor a trace flag?

Ans:

http://blogs.technet.com/b/lobapps/archive/2012/08/28/how-do-i-work-with-trace-flags.aspx

Q. What are the limitations for RAM and CPU for SQL SERVER 2008 R2?

Ans:

Q. Do you know about Resource Database?

Ans:

All sys objects are physically stored in resource database and logically available on every database.

Resource database can faster the service packs or upgrades

Q. Really does resource faster the upgrades? Can you justify?

Ans:

Yes, in earlier versions upgrades requires dropping and recreating system objects now an upgrade requires a copy of the resource file.

We are also capable of rollback the process, because it just needs to overwrite the existing with the older version resource copy.

Q. I have my PROD sql server all system db’s are located on E drive and I need my resource db on H drive how can you move it?

Ans:

No only resource db cannot be moved, Resource db location is always depends on Master database location, if u want to move resource db you should also move master db.

Q. Can we take the backup for Resource DB?

Ans:

No way. The only way if you want to get a backup is use windows backup for option resource mdf and ldf files.

Q. Any idea what is the Resource db mdf and ldf file names?

Ans:

• mssqlsystemresource.mdf and
• mssqlsystemresource.ldf

Q. Can you elaborate the requirements specifications for SQL Server 2008?

Ans:

Q. What you do if a column of data type int is out of scope?

Ans:

I do alter column to BigInt

Q. Are you sure the data type Bigint never been out of scope?

Ans:

Yes I am sure.

Let’s take few examples and see how many years will it take for BIGINT to reach its upper limit in a table:

(A) Considering only positive numbers, Max limit of BIGINT = 9,223,372,036,854,775,807

(B) Number of Seconds in a year = 31,536,000

Assume there are 50,000 records inserted per second into the table. Then the number of years it would take to reach the BIGINT max limit is:

9,223,372,036,854,775,807 / 31,536,000 / 50,000 = 5,849,424 years

Similarly,

If we inserted 1 lakh records per second into the table then it would take 2,924,712 yrs

If we inserted 1 million (1000000) records per second into the table then it would take 292,471 yrs

If we inserted 10 million (10000000) records per second into the table then it would take 29,247 yrs

If we inserted 100 million records per second into the table then it would take 2,925 yrs

If we inserted 1000 million records per second into the table then it would take 292 yrs

By this we would have understood that it would take extremely lots of years to reach the max limit of BIGINT.

Thank You

The post SQL DBA – INTERVIEW QUESTIONS WITH ANSWERS – 2 appeared first on udayarumilli.com.

Performance Tuning – SQL Server  Part – 1

Q. What are the bottlenecks that effects the performance of a Database / Application

Ans:

The top performance bottlenecks for OLTP applications are outlined as:

• Database Design \ Database Code
• Application Design \ Application Code
• CPU bottleneck
• Memory bottleneck
• IO bottleneck
• Blocking bottleneck
• Network bottleneck
• Server Hardware

Database Design \ Database Code

• Too many indexes on frequently updated (inclusive of inserts, updates and deletes):

Tables incur extra index maintenance overhead. Generally, OLTP database designs should keep the number of indexes to a functional minimum, again due to the high volumes of similar transactions combined with the cost of index maintenance

• Statistics may not be updated or missing statistics
• Excess use of cursors and temporary tables
• Too much of normalization
• Do not use the conversion/system/user defined functions in where clause
• Unused indexes incur the cost of index maintenance for inserts, updates, and deletes without benefiting any users:

Unused indexes should be eliminated. Any index that has been used (by select, update or delete operations) will appear in sys.dm_db_index_usage_stats. Thus, any defined index not included in this DMV has not been used since the last re-start of SQL Server

• Choose the Appropriate Data Types

Always choose the smallest appropriate data type. Avoid NCHAR/NVARCHAR unless there is a need of storing Unicode.

• Use Triggers Cautiously

Keep the code in your triggers to the very minimum to reduce overhead. The more code that runs in the trigger, the slower each INSERT, UPDATE, and DELETE that fires it will be

• Don’t Access More Data Than You Need

Don’t return more columns or rows of data to the client than absolutely necessary. This just increases disk I/O on the server

• Avoid Using Cursors
• Wherever possible Try to use alternative solutions includes Temp-Tables, Derived tables, Table Variables or Recursive CTE’s etc
• Always select the cursor with the least amount of overhead. The most efficient cursor you can choose is the fast forward-only cursor.
• When you are done using a cursor, don’t just CLOSE it, DEALLOCATE
• Use Joins Appropriately
• If you have two or more tables that are frequently joined together, then the columns used for the joins should have an appropriate index. If the columns used for the joins are not naturally compact, then considering adding surrogate keys to the tables that are compact in order to reduce the size of the keys, thus decreasing read I/O during the join process, and increasing overall performance. You will learn more about indexing in the next section of this article.
• For best performance, the columns used in joins should be of the same data types. And if possible, they should be numeric data types rather than character types.
• Avoid joining tables based on columns with few unique values. If columns used for joining aren’t mostly unique, then the SQL Server optimizer will perform a table scan for the join, even if an index exists on the columns. For best performance, joins should be done on columns that have unique indexes.
• If you have to regularly join four or more tables to get the recordset you need, consider denormalizing the tables so that the number of joined tables is reduced. Often, by adding one or two columns from one table to another, joins can be reduced.
• Generally, frequent operations requiring 5 or more table joins should be avoided by redesigning the database

• Encapsulate Your Code in Stored Procedures
• Try to put all your T-SQL code in stored procedures which reduces the network traffic by just calling the proc from application and reduces the I/O overhead by using the compiled execution plan
• Always use the option “SET NOCOUNT ON”
• Design the proc’s to avoid the deadlocks
• Collect all inputs before the transaction begins
• Keep transaction short with in a batch
• Use the correct isolation levels
• Try to use with no lock option

Application Design / Application code:

Application Design issues:

• Perform as many data-centered tasks as possible on SQL Server in the form of stored procedures. Avoid manipulating data at the presentation and business services tiers.
• Don’t maintain state (don’t store data from the database) in the business services tier. Maintain state in the database as much as possible
• Don’t create complex or deep object hierarchies. The creation and use of complex classes or a large number of objects used to model complex business rules can be resource intensive and reduce the performance and scalability of your application. This is because the memory allocation when creating and freeing these objects is costly.
• Consider designing the application to take advantage of database connection pooling and object pooling using Microsoft Transaction Server (MTS). MTS allows both database connections and objects to be pooled, greatly increasing the overall performance and scalability of your application.
• If your application runs queries against SQL Server that by nature are long, design the application to be able to run queries asynchronously. This way, one query does not have to wait for the next before it can run. One way to build in this functionality into your n-tier application is to use the Microsoft Message Queue Server (MSMQ).

Application Code:

• Use OLE DB to Access SQL Server:
  • You can access SQL Server data using either ODBC or OLE DB. For best performance, always select OLE DB. OLE DB is used natively by SQL Server, and is the most effective way to access any SQL Server data.
• Use DSN-less in Connection String:
  • While creating an ADO connection to SQL Server, you can either use a DSN in the connection string, or you can use a DSN-less connection. For optimal performance, use DSN-less connections. Using them prevents the need for the OLE DB driver to look up connection string information in the registry of the client the application code is running on, saving some overhead.
• Encapsulate your DML (Data Manipulation Language) in Stored Procedures
  • ADO allows you three different ways to SELECT, INSERT, UPDATE, or DELETE data in a SQL Server database. You can use ADO’s methods, you can use dynamic SQL, or you can use stored procedures. For better performance prefer Stored Procedures
• Encapsulate Your ADO Code in COM Components
  • Put the ADO code that accesses SQL Server data into COM components. This gives you all the standard benefits of COM components, such as object pooling using MTS. And for ASP-based applications, it provides greater speed because the ADO code in COM objects is already compiled, unlike ADO code found in ASP pages. How you implement your data manipulation code in COM components should be considered when the application is first designed.
  • For optimum performance, COM objects should be compiled as in-process DLLs (which is required if they are to run under MTS). You should always employ early binding when referencing COM objects, and create them explicitly, not implicitly.

CPU bottlenecks:

• Signal waits > 25% of total waits.

(See sys.dm_os_wait_stats for Signal waits and Total waits. Signal waits measure the time spent in the runnable queue waiting for CPU. High signal waits indicate a CPU bottleneck.)

• Plan re-use < 90%.

(A query plan is used to execute a query. Plan re-use is desirable for OLTP workloads because re-creating the same plan (for similar or identical transactions) is a waste of CPU resources. Compare SQL Server SQL Statistics: batch requests/sec to SQL compilations/sec. Compute plan re-use as follows: Plan re-use = (Batch requests – SQL compilations) / Batch requests. Special exception to the plan re-use rule: Zero cost plans will not be cached (not re-used) in SQL 2005 SP2. Applications that use zero cost plans will have a lower plan re-use but this is not a performance issue.)

Memory bottleneck:

• Consistently low average page life expectancy. (MSSQL$Instance: Buffer Manager\Page Life Expectancy:)

(See Average Page Life Expectancy Counter which is in the Perfmon object SQL Server Buffer Manager (this represents is the average number of seconds a page stays in cache). For OLTP, an average page life expectancy of 300 is 5 minutes. Anything less could indicate memory pressure, missing indexes, or a cache flush)

• Consistently low SQL Cache hit ratio. (MSSQL$Instance: Plan Cache\Cache Hit Ratio:)

(OLTP applications (e.g. small transactions) should have a high cache hit ratio. Since OLTP transactions are small, there should not be (1) big drops in SQL Cache hit rates or (2) consistently low cache hit rates < 90%. Drops or low cache hit may indicate memory pressure or missing indexes.)

IO bottleneck:

• High average disk seconds per read.

(When the IO subsystem is queued, disk seconds per read increases. See Perfmon Logical or Physical disk (disk seconds/read counter). Normally it takes 4-8ms to complete a read when there is no IO pressure. When the IO subsystem is under pressure due to high IO requests, the average time to complete a read increases, showing the effect of disk queues. Periodic higher values for disk seconds/read may be acceptable for many applications. For high performance OLTP applications, sophisticated SAN subsystems provide greater IO scalability and resiliency in handling spikes of IO activity. Sustained high values for disk seconds/read (>15ms) does indicate a disk bottleneck.)

• High average disk seconds per write.

(See Perfmon Logical or Physical disk. The throughput for high volume OLTP applications is dependent on fast sequential transaction log writes. A transaction log write can be as fast as 1ms (or less) for high performance SAN environments. For many applications, a periodic spike in average disk seconds per write is acceptable considering the high cost of sophisticated SAN subsystems. However, sustained high values for average disk seconds/write is a reliable indicator of a disk bottleneck.)

• Big IOs such as table and range scans due to missing indexes.

Blocking bottleneck:

• High average row lock or latch waits.

(The average row lock or latch waits are computed by dividing lock and latch wait milliseconds (ms) by lock and latch waits. The average lock wait ms computed from sys.dm_db_index_operational_stats represents the average time for each block.)

• Top wait statistics
• High number of deadlocks.

(See Profiler “Graphical Deadlock” under Locks event to identify the statements involved in the deadlock.)

Network bottleneck:

• High network latency coupled with an application that incurs many round trips to the database.
• Network bandwidth is used up.

(See counters packets/sec and current bandwidth counters in the network interface object of Performance Monitor. For TCP/IP frames actual bandwidth is computed as packets/sec * 1500 * 8 /1000000 Mbps)

Server Hardware:

Most slow applications are slow because of poor up front design, not because of slow hardware. Since the application’s design can’t be changed at the time when deployed to production, about the only thing you can try to help boost performance is to throw hardware at it.

• CPU: Always purchase a server with the ability to expand its number of CPUs. Usually it goes for larger servers with four or more CPUs. Always leave room for growth.
• Memory: Try to get enough RAM to hold the largest table you expect to have, and if you can afford it, get all the RAM your server can handle, which is often 2GB or more.
• I/O Subsystem: At the very minimum, purchase hardware-based RAID for your databases. As a rule of thumb, you will to purchase more – smaller drives, not fewer – larger drives in your array. The more disks that are in an array, the faster I/O will be.
• Network Connection: At the server, have at least one 100Mbs network card, and it should be connected to a switch. Ideally, you should have two network cards in the server connected to a switch in full-duplex mode.

For best performance on a server, SQL Server should be the only application running on the server, other than management utilities. Don’t try to save a few bucks by putting your IIS server on the same server as SQL Server.

Q. What is the process of tuning the Performance?

Ans:

• Identification – Use native tools like Profiler, Query Tuning Advisor, Query Execution Plans, Performance Monitor, system stored procedures, dynamic management views, custom stored procedures or third party tools
• Analysis – Analyze the data to determine the core problems
• Providing Solution -
• Creating new index on appropriate columns
• Altering the complex quires to make them use the existing indexes.
• By Updating Statistics for Tables and Views.
• By Rebuilding and Reorganizing indexes.
• By Resolving blocking problems.
• By removing Deadlocks.
• Testing – Test the various options to ensure they perform better and do not cause worse performance in other portions of the application
• Knowledge sharing – Share your experience with the team to ensure they understand the problem and solution, so the issue does not occur again

Q. How to choose the correct (Clustered/ Non- Clustered) index on a column?

Ans:

Selecting Clustered Index:

• Clustered indexes are ideal for queries that select by a range of values or where you need sorted results. Examples of this include when you are using BETWEEN, <, >, GROUP BY, ORDER BY, and aggregates such as MAX, MIN, and COUNT in your queries.
• Clustered indexes are good for queries that look up a record with a unique value (such as an employee number) and when you need to retrieve most or all of the data in the record.
• Clustered indexes are good for queries that access columns with a limited number of distinct values, such as columns that holds country or state data. But if column data has little distinctiveness, such as columns with a yes or no, or male or female, then these columns should not be indexed at all.
• Avoid putting a clustered index on columns that increment, such as an identity, date, or similarly incrementing columns, if your table is subject to a high level of INSERTS.

Selecting Non – Clustered Index:

• Non-clustered indexes are best for queries that return few rows (including just one row) and where the index has good selectivity (above 95%).
• If a column in a table is not at least 95% unique, then most likely the SQL Server Query Optimizer will not use a non-clustered index based on that column. For example, a column with “yes” or “no” as the data won’t be at least 95% unique.
• Keep the “width” of your indexes as narrow as possible, especially when creating composite (multi-column) indexes. This reduces the size of the index and reduces the number of reads required to read the index, boosting performance.
• If possible, try to create indexes on columns that have integer values instead of characters. Integer values have less overhead than character values.
• If you know that your application will be performing the same query over and over on the same table, consider creating a covering index on the table. A covering index includes all of the columns referenced in the query.
• An index is only useful to a query if the WHERE clause of the query matches the column(s) that are leftmost in the index. So if you create a composite index, such as “City, State”, then a query such as “WHERE City = ‘Houston'” will use the index, but the query “WHERE STATE = ‘TX'” will not use the index.

Q. How to read the graphical execution plan?

Ans:

The plan should be read from right to left

• Check the Graphical execution plan of a stored procedure / Query
• Table Scan – Index is missing
• Index Scan – Proper indexes are not using
• BookMark Lookup – Limit the number of columns in the select list
• Filter – Remove any functions from where clause, May require additional indexes
• Sort – Does the data really need to be sorted? Can an index be used to avoid sorting? Can sorting be done at the client more efficiently?
• DataFlow Arrow – High density: Sometimes you find few rows as outcome but the arrow line density indicates the query/proc processing huge number of rows
• Cost – Can easily find out which table / operation taking much time
• From the execution plan we can find out the bottleneck and give the possible solution to avoid the latency

Q. Why the Actual and Estimated Execution Plans Might Differ

Ans

• When Statistics are Stale:

The main cause of a difference between the plans is differences between the statistics and the actual data. This generally occurs over time as data is added and deleted.

• When the Estimated plan is invalid:

When the batch contains temporary tables or the T-SQL statements which refers some of the objects that are not currently existed in the database, but will be created once the batch is run. (Create table is there in batch)

Q. What are the permissions required to view execution plans?

Ans:

Either the user must be mapped to sysadmin, db_owner, db_creator or he/she will be granted the permission “Show Plan”.

GRANT SHOWPLAN TO [username]

Q. What are the tools available for performance tuning/monitoring?

Ans:

• Performance Studio: Act as a Central Data Repository, Collect Selected SQL Server Performance Data and Display Performance Reports
• Activity Monitor: It displays graphically about Processes, Resource Waits, Datafile I/O, Recent expensive Quires.
• Database Tuning Advisor (DTA): Recommend indexes
• Profiler: Can run traces and find out the expensive/long running quires/transactions
• Execution Plans: There are three types Graphical, Text and XML.
• DMV: Dynamic management views shows the current state of the sql server
• PerfMon: Windows native tool to view / monitor the performance of both sql and windows servers
• Third Party: Redgate products

Q. How to identify the CPU bottlenecks and how to resolve it?

Ans:

Identifying CPU Bottlenecks:

Firstly we have to confirm that SQL Server – CPU utilization is high. Run the below query

SELECT Timestamp, CONVERT(XML, record) AS XmlRecord

FROM SYS.DM_OS_RING_BUFFERS

WHERE ring_buffer_type = N’RING_BUFFER_SCHEDULER_MONITOR’

AND record like ‘%<SystemHealth>%’

ORDER BY timestamp DESC

One record is stored every minute up to a maximum of 256 records. Clicking on any of the XML links will take you to the XML editor and will show an entry similar to below

<Record id=”434″ type=”RING_BUFFER_SCHEDULER_MONITOR” time=”22398046″>

<SchedulerMonitorEvent>

<SystemHealth>

<ProcessUtilization>55</ProcessUtilization>

<SystemIdle>35</SystemIdle>

<UserModeTime>228180000</UserModeTime>

<KernelModeTime>251812000</KernelModeTime>

<PageFaults>64252</PageFaults>

<WorkingSetDelta>21770240</WorkingSetDelta>

<MemoryUtilization>100</MemoryUtilization>

</SystemHealth>

</SchedulerMonitorEvent>

</Record>

Information from above XML:

ProcessUtilization: Percentage of CPU utilized by SQL Server – 55%

SystemIdle: Percentage of Idle CPU – 35%

Other processes using CPU: 100- (55+35) = 10 %

Now find out the query/proc/process that is making CPU utilization High:

SELECT TOP 20

qst.sql_handle,

qst.execution_count,

qst.total_worker_time AS Total_CPU,

total_CPU_inSeconds = –Converted from microseconds

qst.total_worker_time/1000000,

average_CPU_inSeconds = –Converted from microseconds

(qst.total_worker_time/1000000) / qst.execution_count,

qst.total_elapsed_time,

total_elapsed_time_inSeconds = –Converting from microseconds

qst.total_elapsed_time/1000000,

st.text AS ‘Query’,

qp.query_plan

from

sys.dm_exec_query_stats as qst

CROSS APPLY sys.dm_exec_sql_text(qst.sql_handle) as st

cross apply sys.dm_exec_query_plan (qst.plan_handle) as qp

ORDER BY qst.total_worker_time DESC

From the above script we can find the commands which are taking the most CPU time along with the execution plan. By reviewing the execution plan you can see what additional indexes need to be added to the database which will improve database performance and decrease the CPU load time.

By adding missing indexes or by using the proper indexes we can decrease the load on CPU.

Other options:

• Sp_monitor: Displays statistics, including CPU usage, I/O usage, and the amount of time idle since sp_monitor was last executed. We can get the information about the “CPU Time (Sec)”, “I/O Time (Sec)”, “Count of Input\Output Packets”, “No of logins attempted”, “Errors in reading/writing network packets” etc.
• @@CPU_BUSY / @@IO_BUSY: Returns the time that SQL Server has spent working since it was last started. Result is in CPU time increments, or “ticks,” and is cumulative for all CPUs, so it may exceed the actual elapsed time. Multiply by @@TIMETICKS to convert to microseconds. But it may not the accurate value to be considered.
• PerfMon
• Profiler

Q. Can you tell me what the Wait Type “LAZY WRITTER” is?

Ans:

The job of the lazy writer is to find dirty pages in the buffer pool and write them out to disk and drop those pages from cache.

Q. Can we find performance bottleneck from sysprocesses?

Ans:

Yes. We may not confirm that it is the only bottleneck but at least we can find the bottleneck. Lastwaittype column with waittime plays a vital role in identifying the issue. This is a very interesting column because it can tell you what the offending query is waiting for to complete.

Network_io: There is too much of traffic in Network

Cxpacket: Your process is waiting on other parallel processes to complete.

SOS_SCHEDULER_YIELD: CPU bound. We may not have enough CPU in your box

IO_Completion: Disk issue. We may not have enough disk space or running on corrupted disk array.

Q. What Are SQL Server Waits?

Ans:

Instead of measuring activity of CPU, storage, or memory, why not ask what SQL Server has been waiting on when executing queries?

In general there are three categories of waits that could affect any given request:

• Resource waits are caused by a particular resource, perhaps a specific lock that is unavailable when the requested is submitted.
• External waits occur when SQL Server worker thread is waiting on an external process
• Queue waits normally apply to internal background tasks, such as ghost cleanup, which physically removes records that have been previously deleted.

Q. How could you know the statistics are outdated?

Ans:

If old statistics is your problem, you will likely experience this as a gradual decline of SQL Server slowing down over many days or weeks, or you may have just upgraded your platform (from 2000 to 2008) and forgot to update the statistics. Out of date statistics cause inaccurate execution plans.

Q. What are the main parameters we need to check when you are dealing with memory performance?

Ans:

There are four significant properties of sql server.

Max server memory and Min server memory:

Use the two server memory options, min server memory and max server memory, to reconfigure the amount of memory (in megabytes) that is managed by the SQL Server Memory Manager for a SQL Server process used by an instance of SQL Server. By default Min Memory is set to be 0 and Max Memory is set to be 2147483647 MB (21 GB). Never leave these two settings as default. Depends on the memory available and other applications running on windows Server, change these two settings.

For example we have 24 GB available and the settings can be like this:

Min Memory: 1 GB

Max Memory: 16 GB

Remember total max memory of all instances should not exceeds the actual physical memory available

Priority boost: By default, the priority boost setting is 0, which causes SQL Server to run at a normal priority. If you set priority boost to 1, the SQL Server process runs at a high priority.

Lightweight pooling: Switch on this parameter when you want to make sql server use the fiber mode facility. Unless there is a real need and environment (Large multi-processor servers) available we should not use this option at production servers.

The post SQL Server Performance Tuning Interview Questions – Part 1 appeared first on udayarumilli.com.

Performance Tuning – SQL Server Part -2 – Indexes

Q. What are the primary differences between an index reorganization and an index rebuild?

Ans:

• Reorganization is an “online” operation by default; a rebuild is an “offline” operation by default
• Reorganization only affects the leaf level of an index
• Reorganization swaps data pages in-place by using only the pages already allocated to the index; a rebuild uses new pages/allocations
• Reorganization is always a fully-logged operation; a rebuild can be a minimally-logged operation
• Reorganization can be stopped mid-process and all completed work is retained; a rebuild is transactional and must be completed in entirety to keep changes

Q. During an index reorganization operation, if the index spans multiple files, will pages be allowed to migrate between files

Ans:

No – pages will not migrate between files during an index reorganization.

Q. If you need to REBUILD a non-clustered index that is 10GB in size and have 5GB of free data-file space available with no room to grow the data file(s), how can you accomplish the task?

Ans:

When rebuilding an existing non-clustered index, you typically require free space that is approximately equivalent to 2.2 times the size of the existing index, since during a rebuild operation, the existing index is kept until the rebuilt structure is complete and an additional approximately 20% free space for temporary sorting structures used during the rebuild operation

• In this case, you would require at least an additional 10+ GB of free space for the rebuild operation to succeed, since the index itself is 10GB in size.
• Using SORT_IN_TEMPDB would not suffice in this case, since only the temporary sort tables are stored in tempdb in this case, and at least 10 GB of free space would still be required in the database data files.

Your possibilities are different for SQL Server2000 vs. SQL Server 2005/2008:

• In SQL Server 2000, you only have 1 option in this case.  Drop the index and recreate it.
• In SQL Server 2005/2008, you can do the same as you did with SQL Server 2000 (drop, recreate), but you also have another option. If you first disable the index (via the ALTER INDEX…DISABLE statement) the existing space consumed by the index will be freed. Then running a simple ALTER INDEX…REBUILD command will allow the build operation to use the now 15gb of free space to build the index.

Q. What is the Covering Index?

Ans:

If you know that your application will be performing the same query over and over on the same table, consider creating a covering index on the table. A covering index, which is a form of a composite non clustered index, includes all of the columns referenced in SELECT, JOIN, and WHERE clauses of a query. Because of this, the index contains the data you are looking for and SQL Server doesn’t have to look up the actual data in the table, reducing logical and/or physical I/O, and boosting performance.

On the other hand, if the covering index gets too big (has too many columns), this could actually increase I/O and degrade performance.

Q. What is Online Indexing?

Ans:

Online Indexing is a new feature available in SQL Server 2005. In SQL Server 2005, DBAs can create, rebuild, or drop indexes online. The index operations on the underlying table can be performed concurrently with update or query operations. This was not possible in previous versions of SQL Server. In the past, indexing operations (reorganizing or rebuilding) were usually performed as a part of other maintenance tasks running during off-peak hours. During these offline operations, the indexing operations hold exclusive locks on the underlying table and associated indexes. During online index operations, SQL Server 2005 eliminates the need of exclusive locks

The Online indexing feature is very helpful for environments that run 24 hours a day, seven days a week. The Online Indexing feature is available only in the Enterprise Edition of SQL Server 2005/2008.

Q. How Online Indexing works?

Ans:

The online index operation can be divided into three phases:

• Preparation
• Build
• Final

The Build phase is a longest phase of all. It is in this phase where the creation, dropping, or rebuilding of indexes take place. The duration of the Build phase depends on the size of the data and the speed of the hardware. Exclusive locks are not held in this phase, so concurrent DML operations can be performed during this phase. The Preparation and Final phases are for shorter durations. They are independent of the size factor of the data. During these two short phases, the table or the indexed data is not available for concurrent DML operations.

Q. How to know unused indexes in a table.

Ans:

By using a DMV we‘ll find the unused indexes details. We have a DMV called “sys.dm_db_index_usage_stats” which retrieves the statistics of indexes , if an index id is not in that dmv then we can say that index is not been using from a long time.

Q. What are the index limitations?

Ans:

INDEXTYPE – 32 BIT / 64 BIT

NON CLUSTERED – 999 / 999

XML indexes 249 / 249

Columns per index key – 16 / 16 – Only 900 Byte

Q. What are the different indexes available?

Ans:

Index Types

• Clustered Index: A clustered index sorts and stores the data rows of the table or view in order based on the clustered index key. The clustered index is implemented as a B-tree index structure that supports fast retrieval of the rows, based on their clustered index key values.
• Non Clustered Index: A nonclustered index can be defined on a table or view with a clustered index or on a heap. Each index row in the nonclustered index contains the nonclustered key value and a row locator. This locator points to the data row in the clustered index or heap having the key value. The rows in the index are stored in the order of the index key values, but the data rows are not guaranteed to be in any particular order unless a clustered index is created on the table.
• Unique Index: An index that ensures the uniqueness of each value in the indexed column. If the index is a composite, the uniqueness is enforced across the columns as a whole, not on the individual columns. For example, if you were to create an index on the FirstName and LastName columns in a table, the names together must be unique, but the individual names can be duplicated. A unique index is automatically created when you define a primary key or unique constraint:
  • Primary key: When you define a primary key constraint on one or more columns, SQL Server automatically creates a unique, clustered index if a clustered index does not already exist on the table or view. However, you can override the default behavior and define a unique, nonclustered index on the primary key.
  • Unique: When you define a unique constraint, SQL Server automatically creates a unique, nonclustered index. You can specify that a unique clustered index be created if a clustered index does not already exist on the table.
• Index with Included Columns: A nonclustered index that is extended to include nonkey columns in addition to the key columns. They can be data types not allowed as index key columns. They are not considered by the Database Engine when calculating the number of index key columns or index key size. Need to use INCLUDE clause while creating index.
• Full Text Indexes: A special type of token-based functional index that is built and maintained by the Microsoft Full-Text Engine for SQL Server. It provides efficient support for sophisticated word searches in character string data.
• Spatial Indexes: A spatial index provides the ability to perform certain operations more efficiently on spatial objects (spatial data) in a column of the geometry data type. The spatial index reduces the number of objects on which relatively costly spatial operations need to be applied.
• Filtered Index: An optimized nonclustered index, especially suited to cover queries that select from a well-defined subset of data. It uses a filter predicate to index a portion of rows in the table. A well-designed filtered index can improve query performance, reduce index maintenance costs, and reduce index storage costs compared with full-table indexes. Use where clause in create index statement.
• Composite index: An index that contains more than one column. In both SQL Server 2005 and 2008, you can include up to 16 columns in an index, as long as the index doesn’t exceed the 900-byte limit. Both clustered and nonclustered indexes can be composite indexes.
• XML Indexes: A shredded, and persisted, representation of the XML binary large objects (BLOBs) in the xml data type column.

Q. I have a situation where I need to create an index on 20 columns. Is it practically possible? If yes justify?

Ans:

Yes ! We can create an index on 20 columns using INCLUDE clause.

You can include nonkey columns in a nonclustered index to avoid the current index size limitations of a maximum of 16 key columns and a maximum index key size of 900 bytes. The SQL Server Database Engine does not consider nonkey columns when calculating the number of index key columns or the total size of the index key columns. In a nonclustered index with included columns, the total size of the index key columns is restricted to 900 bytes. The total size of all nonkey columns is limited only by the size of the columns specified in the INCLUDE clause; for example, varchar(max) columns are limited to 2 GB. The columns in the INCLUDE clause can be of all data types, except text, ntext, and image.

Q. On which basis we will create computed indexes?

Ans:

For composite indexes, take into consideration the order of the columns in the index definition. Columns that will be used in comparison expressions in the WHERE clause (such as WHERE FirstName = ‘Charlie’) should be listed first. Subsequent columns should be listed based on the uniqueness of their values, with the most unique listed first.

Q. How to design indexes for a database? Or

What are the index creation best practices?

Ans:

• Understand the characteristics of the database (OLTP / OLAP)
• Understand the characteristics of the most frequently used queries.
• Understand the characteristics of the columns used in the queries.
• Choose the right index at the right place. For example, creating a clustered index on an existing large table would benefit from the ONLINE index option.
• Determine the optimal storage location for the index. A nonclustered index can be stored in the same filegroup as the underlying table, or on a different filegroup. If those filegroups are in different physical drives it will improve the performance.
• Database Considerations:
• Avoid over indexing
• Use many indexes to improve query performance on tables with low update requirements, but large volumes of data.
• Indexing small tables may not be optimal
• Indexes on views can provide significant performance gains when the view contains aggregations and/or table joins. The view does not have to be explicitly referenced in the query for the query optimizer to use it
• Column considerations:
• Keep the length of the index key short for clustered indexes. Additionally, clustered indexes benefit from being created on unique or nonnull columns.
• Columns that are of the ntext, text, image, varchar(max), nvarchar(max), and varbinary(max) data types cannot be specified as index key columns. However, varchar(max), nvarchar(max), varbinary(max), and xml data types can participate in a nonclustered index as nonkey index columns
• Columns that are of the ntext, text, image, varchar(max), nvarchar(max), and varbinary(max) data types cannot be specified as index key columns. However, varchar(max), nvarchar(max), varbinary(max), and xml data types can participate in a nonclustered index as nonkey index columns
• Consider using filtered indexes on columns that have well-defined subsets
• Consider the order of the columns if the index will contain multiple columns. The column that is used in the WHERE clause in an equal to (=), greater than (>), less than (<), or BETWEEN search condition, or participates in a join, should be placed first.
• Index Characteristics: Determine the right index depends on the business need
• Clustered versus nonclustered
• Unique versus nonunique
• Single column versus multicolumn
• Ascending or descending order on the columns in the index
• Full-table versus filtered for nonclustered indexes
• Determine the Fill Factor

Q. Can we create index on table variables?

Yes, Implicitly

Create Index on Table Variable

Creating an index on a table variable can be done implicitly within the declaration of the table variable by defining a primary key and creating unique constraints. The primary key will represent a clustered index, while the unique constraint a non clustered index.

DECLARE @Users TABLE

(

UserID INT PRIMARY KEY,

UserName varchar(50),

UNIQUE (UserName)

)

The drawback is that the indexes (or constraints) need to be unique. One potential way to circumvent this however, is to create a composite unique constraint:

DECLARE @Users TABLE

(

UserID INT PRIMARY KEY,

UserName varchar(50),

FirstName varchar(50),

UNIQUE (UserName,UserID)

)

You can also create the equivalent of a clustered index. To do so, just add the clustered reserved word.

DECLARE @Users TABLE

(

UserID INT PRIMARY KEY,

UserName varchar(50),

FirstName varchar(50),

UNIQUE CLUSTERED (UserName,UserID)

)

Q. What is the Heap Table?

Ans:

HEAP

• Data is not stored in any particular order
• Specific data cannot be retrieved quickly, unless there are also non-clustered indexes
• Data pages are not linked, so sequential access needs to refer back to the index allocation map (IAM) pages
• Since there is no clustered index, additional time is not needed to maintain the index
• Since there is no clustered index, there is not the need for additional space to store the clustered index tree
• These tables have a index_id value of 0 in the sys.indexes catalog view

Q. How to get the index usage information?

Q. Query to retrieve the indexes that are being used?

Ans:

sys.dm_db_index_usage_stats - bind with sysobjects

This view gives you information about overall access methods to your indexes.  There are several columns that are returned from this DMV, but here are some helpful columns about index usage:

• user_seeks – number of index seeks
• user_scans- number of index scans
• user_lookups – number of index lookups
• user_updates – number of insert, update or delete operations

sys.dm_db_index_operational_stats – bind with sysindexes

This view gives you information about insert, update and delete operations that occur on a particular index.  In addition, this view also offers data about locking, latching and access methods.  There are several columns that are returned from this view, but these are some of the more interesting columns:

• leaf_insert_count – total count of leaf level inserts
• leaf_delete_count – total count of leaf level inserts
• leaf_update_count  – total count of leaf level updates

SELECT DB_NAME(DATABASE_ID) AS DATABASENAME,
OBJECT_NAME(B.OBJECT_ID) AS TABLENAME,
INDEX_NAME = (SELECT NAME
FROM   SYS.INDEXES A
WHERE  A.OBJECT_ID = B.OBJECT_ID
AND A.INDEX_ID = B.INDEX_ID),
USER_SEEKS,
USER_SCANS,
USER_LOOKUPS,
USER_UPDATES
FROM   SYS.DM_DB_INDEX_USAGE_STATS B
INNER JOIN SYS.OBJECTS C
ON B.OBJECT_ID = C.OBJECT_ID
WHERE  DATABASE_ID = DB_ID(DB_NAME())
AND C.TYPE <> ‘S’

Q. What is fill factor? How to choose the fill factor while creating an index?

Ans:

The Fill Factor specifies the % of fullness of the leaf level pages of an index. When an index is created or rebuilt the leaf level pages are written to the level where the pages are filled up to the fill factor value and the remainder of the page is left blank for future usage. This is the case when a value other than 0 or 100 is specified.  For example, if a fill factor value of 70 is chosen, the index pages are all written with the pages being 70 % full, leaving 30 % of space for future usage.

Q. When to choose High or Low Fillfactor Value?

Ans:

You might choose a high fill factor value when there is very little or no change in the underlying table’s data, such as a decision support system where data modification is not frequent, but on a regular and scheduled basis. Such a fill factor value would be better, since it creates an index smaller in size and hence queries can retrieve the required data with less disk I/O operations since it has to read less pages.

On the other hand if you have an index that is constantly changing you would want to have a lower value to keep some free space available for new index entries.  Otherwise SQL Server would have to constantly do page splits to fit the new values into the index pages.

Q. What methods are available for removing fragmentation of any kind on an index in SQL Server?

Ans:

SQL Server 2000:

• • DBCC INDEXDEFRAG
  • DBCC DBREINDEX
  • CREATE INDEX…DROP EXISTING (cluster)
  • DROP INDEX; CREATE INDEX

SQL Server 2005 and above: The same processes as SQL Server 2000, only different syntax

• • ALTER INDEX…REORGANIZE
  • ALTER INDEX…REBUILD
  • CREATE INDEX…DROP EXISTING (cluster)
  • DROP INDEX; CREATE INDEX

Q. What page verification options are available in SQL Server and how do they work?

Ans:

SQL Server 2000: Only “Torn Page Detection” is available in SQL Server 2000.

SQL Server 2005:  Both “Torn Page Detection” and “Checksum” page verification options exist in SQL Server 2005.  Page verification checks help to discover damaged database pages caused by disk I/O path errors. Disk I/O path errors can be the cause of database corruption problems and are generally caused by power failures or disk hardware failures that occur at the time the page is being written to disk.

TORN PAGE DETECTION:

Works by saving a specific bit for each 512-byte sector in the 8-kilobyte (KB) database page and is stored in the database page header when the page is written to disk. When the page is read from disk, the torn bits stored in the page header are compared to the actual page sector information. Unmatched values indicate that only part of the page was written to disk. In this situation, error message 824 (indicating a torn page error) is reported to both the SQL Server error log and the Windows event log. Torn pages are typically detected by database recovery if it is truly an incomplete write of a page. However, other I/O path failures can cause a torn page at any time.

CHECKSUM:

Works by calculating a checksum over the contents of the whole page and stores the value in the page header when a page is written to disk. When the page is read from disk, the checksum is recomputed and compared to the checksum value stored in the page header. If the values do not match, error message 824 (indicating a checksum failure) is reported to both the SQL Server error log and the Windows event log. A checksum failure indicates an I/O path problem. To determine the root cause requires investigation of the hardware, firmware drivers, BIOS, filter drivers (such as virus software), and other I/O path components.

Q. What are the primary differences between an index reorganization and an index rebuild?

Ans:

• Reorganization is an “online” operation by default; a rebuild is an “offline” operation by default
• Reorganization only affects the leaf level of an index
• Reorganization swaps data pages in-place by using only the pages already allocated to the index; a rebuild uses new pages/allocations
• Reorganization is always a fully-logged operation; a rebuild can be a minimally-logged operation
• Reorganization can be stopped mid-process and all completed work is retained; a rebuild is transactional and must be completed in entirety to keep changes

Q. During an index reorganization operation, if the index spans multiple files, will pages be allowed to migrate between files

Ans:

No – pages will not migrate between files during an index reorganization.

Q. How to make forcefully use an index in a query? Or What table hint needs to be specified to forcefully use an index in a query?

Ans:

We can specify “Index” table hint in a query to forcefully use an index.

Ex: SELECT Emp_ID, Name FROM Emp WITH(INDEX(NIX_NAME_EMP))

Q. What are the index statistics?

Ans:

Index statistics contain information about the distribution of index key values. By distribution, I mean the number of rows associated with each key value. SQL Server uses this information to determine what kind of execution plan to use when processing a query.

Q. When are index statistics updated?

Ans:

The AUTO_UPDATE_STATISTICS database setting controls when statistics are automatically updated.  Once statistics have been created, SQL Server then determines when to update those statistics based on how out-of-date the statistics might be. SQL Server identifies out of date statistics based on the number of inserts, updates, and deletes that have occurred since the last time statistics were updated, and then recreates the statistics based on a threshold. The threshold is relative to the number of records in the table. (Enable the properties – “auto create statistics” and “auto update statistics” for OLTP)

Q. Explain database options “Auto Update Statistics” and “Auto Update Statistics Asynchronous”?

Ans:

Auto Update Statistics: If there is an incoming query but statistics are stale then sql server first update the statistics before building the execution plan.

Auto Update Statistics Asynchronous: If there is an incoming query but statistics are stale then sql servers uses the stale statistics, builds the execution plan and then update the statistics.

Q. How to update statistics manually?

Ans:

If you want to manually update statistics, you can use either sp_updatestats or UPDATE STATISTICS <statistics name>

Q. What are the various types of statistics available?

Ans:

There are three different types of statistics available.

• Statistics created due to index creation.
• Statistics created by optimizer.
• User defined statistics created from “CREATE STATISTICS”

Q. What are the various options to be considered while designing a new execution plan?

Ans:

There are a number of factors that influence the decision in choosing the proper execution plan. One of the most important ones are cardinality estimations, the process of calculating the number of qualifying rows that are likely after filtering operations are applied. A query execution plan selected with inaccurate cardinality estimates can perform several orders of magnitude slower than one selected with accurate estimates. These cardinality estimations also influence plan design options, such as join-order and parallelism. Even memory allocation, the amount of memory that a query requests, is guided by cardinality estimations.

Other factors that influence the optimizer in choosing the execution plan are:

Q. How histogram built?

Ans:

As we all know that when we index a column, SQL Server does two things:

1. Sorts the values of the column in an internal data structure called “Index” This data structure contains the sorted value and a pointer to its respective row in the table.
2. Generates a histogram of values.

The histogram shows the distribution of values for the sorted column. For example:

if we have following values in an integer column 1,2,2,3,4,1,4,5,4 then a typical histogram will be similar to this

So suppose if you are searching for all rows having column values between 3 and 5 then by looking at the above histogram table you can estimate that you will get total 1+3+1=5 rows.  If your table contains just 9 rows in total then 5 rows means approximately 55% of total rows will match the criteria. Based on this calculation you may elect to directly scan the table instead of first reading the index, fetching the pointers of the matching rows and then read the actual rows. Although, it is a very simple example and there are other factors involve in deciding whether to use index or not but this example demonstrates the concept in very simple terms.

Q. How to find out when statistics updated last time?

Ans:

A simple logic is, run the query and observe the values for both “estimated rows” and “actual rows”, if they both are close to each other you need not worried about the statistics. If you find big difference between them then you need to think about updating statistics.

In general we can find out last statistics updated info from below query

select object_name(object_id) as table_name

,name as stats_name

,stats_date(object_id, stats_id) as last_update

from sys.stats

where objectproperty(object_id, ‘IsUserTable’) = 1

order by last_update

Q. What is RID Lookup \ Bookmark Lookup?

Ans:

RID lookup will be seen when you use non-clustered indexes with join queries.

In order to understand the RID look up we need to first understand how non-clustered indexes work with clustered indexes and heap tables. Below is a simple figure which describes the working and their relationships.

Non-clustered indexes also use the B-tree structure fundamental to search data. In non-clustered indexes the leaf node is a ‘Rowid’ which points to different things depending on two scenarios:-

Scenario 1:- If the table which is having the primary key in the join has a clustered index on the join key then the leaf nodes i.e. ‘rowid’ will point to the index key of clustered index hence a clustered index seek happens

Scenario 2 :- if the table which is having the primary does not have a clustered index then the non-clustered index leaf node ‘rowid’ will point to actual row on the heap table. As the data is stored in a different heap table, it uses the lookup (i.e. RID lookup) to get to the actual row hence an Index seek (Non clustered) with RID lookup happens

The post SQL Server Performance Tuning Interview Questions – Part 2 – Indexes appeared first on udayarumilli.com.

Performance Tuning – SQL Server Part – 3 – TempDB

Q. Tempdb is filling up drastically, what might be the activity that filling up the tempdb?

Ans:

Usually, tempdb fills up when you are low on disk space, or when you have set an unreasonably low maximum size for database growth.

Many people think that tempdb is only used for #temp tables. When in fact, you can easily fill up tempdb without ever creating a single temp table. Some other scenarios that can cause tempdb to fill up:

• Any sorting that requires more memory than has been allocated to SQL Server will be forced to do its work in tempdb
• DBCC CheckDB(‘any database’) will perform its work in tempdb — on larger databases, this can consume quite a bit of space
• DBCC DBREINDEX or similar DBCC commands with ‘Sort in tempdb’ option set will also potentially fill up tempdb
• Large resultsets involving unions, order by / group by, cartesian joins, outer joins, cursors, temp tables, table variables, and hashing can often require help from tempdb
• Any transactions left uncommitted and not rolled back can leave objects orphaned in tempdb
• Use of an ODBC DSN with the option ‘create temporary stored procedures’ set can leave objects there for the life of the connection
• Table value functions that pull large data sets hold their data in tempdb
• If you are using Snapshot isolation on a database with a high number of transactions the snapshot data is stored in tempdb

Q. How to analyze the TempDB contention

Ans:

• Run the below command

USE tempdb

GO
SELECT table_name FROM information_schema.tables

If you have a few tables, then you are most likely dealing with a large set issue. If you have a very large number of tables, then there is a runaway process or an unclosed process.

• Find the size of the tables. Shortlist the biggest tables and depends on the type of table we can find out the source.
• Make sure that disk space is not full and capacity settings for tempdb (low size for max growth)

Also with queries that fail to use an index on large tables can cause this from time to time. Do you have autoshrink turned on for tempdb

• You could check in on your record locking strategies for your executable sessions and/or records might not be getting released properly. Use the query optimizer tools maybe
• Check for index rebuilding jobs, data pulling jobs/triggers blocking sessions, long running transactions
• Use profiler / perfmon / dbcc commands to find the bottlenecks
• You can use Profiler to watch for events like database file auto grow and log file auto grow. If this is happening often, then you know that the space you’ve allocated to tempdb is not sufficient.
• You can also watch performance monitor’s counter for PhysicalDisk: CurrentDiskQueueLength on the drive where tempdb exists. If this number is consistently greater than 2, then there is likely a bottleneck in disk I/O.

Q. How to fix the TempDB filling issue?

Ans:

Short-Term Fix:

• Shrink Tempdb: We can shrink the db using ShrinkDatabase, DBCC ShrinkFile. If you can’t shrink the log, it might be due to an uncommitted transaction.
• See if you have any long-running transactions with the following command “dbcc opentran(tempdb)”
• Check the oldest transaction (if it returns any), and see who the SPID is “DBCC INPUTBUFFER(SPID)”
• Query will help you determine if you want to end this process with “KILL SPID”

• Restarting SQL Server will re-create tempdb from scratch, and it will return to its usually allocated size. In and of itself, this solution is only effective in the very short term; assumedly, the application and/or T-SQL code which caused tempdb to grow once will likely cause it to grow again.

Long-Term Prevention:

• Make sure that tempdb is set to autogrow — do *NOT* set a maximum size for tempdb. If the current drive is too full to allow autogrow events, then buy a bigger drive, or add files to tempdb on another device (using ALTER DATABASE) and allow those files to autogrow.
• For optimal performance, make sure that its initial size is adequate to handle a typical workload (autogrow events can cause performance to suffer as it allocates new extents).
• If possible, put tempdb on its own physical disk, array or disk subsystem
• To prevent tempdb log file growth, make sure tempdb is in simple recovery mode
• Try to make sure you have covering indexes for all large tables that are used in queries that can’t use a clustered index / index seek.
• In general, try to make your code as efficient as possible… avoid cursors, nested loops, and #temp tables if possible.
• Make sure all the transactions are having the corresponding Commit and Rollback

Q. The most common argument I heard is table variables are in-memory structures (stored in memory not on tempdb) not like temporary tables. Is that true? How can you justify?

Ans:

It’s actually a wrong assumption; both table variables and temp tables are stored in tempdb. A DMV “sys.dm_db_session_space_usage” can help us to make sure these objects use Temdb.

On a development machine restart the SQL server and select data from above DMV as below.

SELECT session_id,

database_id,

user_objects_alloc_page_count

FROM sys.dm_db_session_space_usage

WHERE session_id > 50 ;

Initially user_objects_alloc_page_count is shown as 0.

Create a simple temporary table and insert test data and now check the same DMV, we can see the page_count as 1.

Then create a table variable and insert a row and we can see the page_count increased to 2.

Q. What database objects are stored in tempdb?

Ans:

There are three different types of objects stored in tempdb.

Internal Objects:

1. Intermediate runs for sort.
2. Intermediate results for hash join and hash aggregates.
3. XML variables or other large object (LOB) data type variables. (text, image, ntext, varchar(max), varbinary(max))
4. Queries that need a spool to store intermediate results.
5. Keyset cursors to store the keys.
6. Static cursors to store a query result.
7. Service Broker to store messages in transit.
8. INSTEAD OF triggers to store data for internal processing.
9. DBCC CHECK internally uses a query that may need to spool intermediate results.
10. Query notification and event notification use Service Broker.

Note:

Page allocations on internal objects and Updates to internal objects do not generate log records.

Does not appear in catalog views such as sys.all_objects

Version Store:

1. Snapshot Isolation / Read Committed Snapshot Islotaion
2. Triggers (After Triggers). Instead of triggers doesn’t generate versions.
3. MARS (Multiple Active Result Sets)
4. Index Rebuilds

Note:

Inserts into version stores do not generate log records.

Does not appear in catalog views such as sys.all_objects

User Objects:

1. User defined tables and indexes
2. Local and global temporary tables, bulk insert and BCP intermediate results
3. Index rebuilds with “SORT IN TEMPDB” option.

Note:

Most of the operations under this category are bulk logged.

Appear in catalog views such as sys.all_objects.

The post SQL Server Performance Tuning Interview Questions – Part 3 – TempDB appeared first on udayarumilli.com.

Brad McGehee

Good morning Folks, I have gone through an article which is from Brad’s library.

We should appreciate him for giving us the best article on Indexes.

By understanding this Article we can get some extra knowledge on below

1. What is a Table?
2. What is an Index?
3. Types of data pages
4. What is a Heap?
5. Types of Indexes

We might have gone through various blogs on above topics, but this article will explore at least few new things for sure.

Apart from Indexes we can have a look at below:

Heap and B-Tree structures contain one or more allocation units. This is just a fancy way of subdividing different data types into three categories, which are:

In_Row_Data: This is the most common type of allocation unit, and is used to store data and index pages, except for Large Object (LOB) data. In other words, most of your row data (and related indexes) are stored in this type of allocation unit.

Lob_Data: Used to store Large Object (LOB) data, such as text, ntext, xml, image, varchar(max), nvarchar(max), varbinary(max), and CLR user-defined data types.

Row_Overflow_Data: Used to store data pages when the variable data types—varchar, nvarchar, varbinary, and sql_variant data columns—that exceeds the 8,060 bytes that can fit onto a single data page.

Why are extents used to group eight 8K pages?

Extents are used because it is more resource efficient for SQL Server to allocate eight, 8K pages in a single step than it is for SQL Server to create eight, 8K pages in eight separate steps. There are two types of extents: uniform and mixed extents. All eight pages of a uniform extent are all owned by the same object. In a mixed extent, each page of the extent can be owned by a different object.

Why are there two different kinds of extents?

This is because many objects in a database are less than 64K in size. If only uniform extends were allowed, then there would be a lot of wasted space on extents that are not fully used by an object. By allowing mixed extends, multiple, smaller objects can all fit onto a single extent, which makes more efficient use of available space. Whenever a new table or index is created, it generally is first created on a mixed extent.

What happens if an object on a mixed event grows to exceed 64K?

If that happens, all future page allocations are done using uniform extents.

Here is the Full article:

The post Index Internals appeared first on udayarumilli.com.