FIX: A performance issue in which you run a query by using a Fast Forward cursor in SQL Server 2005 or SQL Server 2008

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Article ID: 973877 - View products that this article applies to.
Microsoft distributes Microsoft SQL Server 2005 fixes as one downloadable file. Because the fixes are cumulative, each new release contains all the hotfixes and all the security fixes that were included with the previous SQL Server 2005 fix release.
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SYMPTOMS

You run a query by using a Fast Forward cursor in Microsoft SQL Server 2005 or SQL Server 2008. However, the query takes a much longer to open the cursor than when you run the same query by using a static cursor.

If you analyze the statistical information about how much disk activity is generated by the query while the cursor is being opened, you may notice the following characteristics:
  • The "read-ahead reads" number is 0 when you use the Fast Forward cursor.
  • The "read-ahead reads" number is a large number when you use a static cursor.


Note You can use the SET STATISTICS IO ON statement to display the statistical information.

CAUSE

When a static cursor is opened, the Read-Ahead mechanism is enabled. However, when a Fast Forward cursor is opened, the Read-Ahead mechanism is disabled. This behavior causes the performance issue that is described in the "Symptoms" section.

RESOLUTION

SQL Server 2005

The fix for this issue was first released in Cumulative Update 5 for SQL Server 2005 Service Pack 3. For more information about this cumulative update package, click the following article number to view the article in the Microsoft Knowledge Base:
972511 Cumulative update package 5 for SQL Server 2005 Service Pack 3
Note Because the builds are cumulative, each new fix release contains all the hotfixes and all the security fixes that were included with the previous SQL Server 2005 fix release. Microsoft recommends that you consider applying the most recent fix release that contains this hotfix. For more information, click the following article number to view the article in the Microsoft Knowledge Base:
960598 The SQL Server 2005 builds that were released after SQL Server 2005 Service Pack 3 was released
Microsoft SQL Server 2005 hotfixes are created for specific SQL Server service packs. You must apply a SQL Server 2005 Service Pack 3 hotfix to an installation of SQL Server 2005 Service Pack 3. By default, any hotfix that is provided in a SQL Server service pack is included in the next SQL Server service pack.

SQL Server 2008

SQL Server 2008

Important You must use this fix if you are running the release version of SQL Server 2008.

The fix for this issue was first released in Cumulative Update 7. For more information about how to obtain this cumulative update package for SQL Server 2008, click the following article number to view the article in the Microsoft Knowledge Base:
973601 Cumulative update package 7 for SQL Server 2008
Note Because the builds are cumulative, each new fix release contains all the hotfixes and all the security fixes that were included with the previous SQL Server 2008 fix release. We recommend that you consider applying the most recent fix release that contains this hotfix. For more information, click the following article number to view the article in the Microsoft Knowledge Base:
956909 The SQL Server 2008 builds that were released after SQL Server 2008 was released

SQL Server 2008 Service Pack 1 (SP1)

Important You must use this fix if you are running SQL Server 2008 Service Pack 1 (SP1).

The fix for this issue was first released in Cumulative Update 4 for SQL Server 2008 Service Pack 1. For more information about this cumulative update package, click the following article number to view the article in the Microsoft Knowledge Base:
973602 Cumulative update package 4 for SQL Server 2008 Service Pack 1
Note Because the builds are cumulative, each new fix release contains all the hotfixes and all the security fixes that were included with the previous SQL Server 2008 fix release. Microsoft recommends that you consider applying the most recent fix release that contains this hotfix. For more information, click the following article number to view the article in the Microsoft Knowledge Base:
970365 The SQL Server 2008 builds that were released after SQL Server 2008 Service Pack 1 was released
Microsoft SQL Server 2008 hotfixes are created for specific SQL Server service packs. You must apply a SQL Server 2008 Service Pack 1 hotfix to an installation of SQL Server 2008 Service Pack 1. By default, any hotfix that is provided in a SQL Server service pack is included in the next SQL Server service pack.

STATUS

Microsoft has confirmed that this is a problem in the Microsoft products that are listed in the "Applies to" section.

MORE INFORMATION

The Database Engine supports a performance optimization mechanism that is named Read-Ahead. The Read-Ahead mechanism predicts the data and index pages that are required to fulfill a query execution plan. Then, the Read-Ahead mechanism brings the pages into the buffer cache before the pages are actually used by the query. This allows for computation and I/O to overlap, taking full advantage of the CPU and the disk.

REFERENCES

For more information about the Incremental Servicing Model for SQL Server, click the following article number to view the article in the Microsoft Knowledge Base:
935897 An Incremental Servicing Model is available from the SQL Server team to deliver hotfixes for reported problems
For more information about how to obtain SQL Server 2005 Service Pack 3, click the following article number to view the article in the Microsoft Knowledge Base:
913089 How to obtain the latest service pack for SQL Server 2005
For more information about the new features in SQL Server 2005 Service Pack 3 (SP3) and about the improvements in SQL Server 2005 SP3, visit the following Microsoft Web site:
http://go.microsoft.com/fwlink/?LinkId=131442
For more information about the naming schema for SQL Server updates, click the following article number to view the article in the Microsoft Knowledge Base:
822499 New naming schema for Microsoft SQL Server software update packages
For more information about software update terminology, click the following article number to view the article in the Microsoft Knowledge Base:
824684 Description of the standard terminology that is used to describe Microsoft software updates

Properties

Article ID: 973877 - Last Review: August 17, 2009 - Revision: 1.2
APPLIES TO
  • Microsoft SQL Server 2005 Standard Edition
  • Microsoft SQL Server 2005 Enterprise Edition
  • Microsoft SQL Server 2005 Standard X64 Edition
  • Microsoft SQL Server 2005 Enterprise X64 Edition
  • Microsoft SQL Server 2005 Standard Edition for Itanium-based Systems
  • Microsoft SQL Server 2005 Enterprise Edition for Itanium-based Systems
  • Microsoft SQL Server 2005 Developer Edition
  • Microsoft SQL Server 2005 Workgroup Edition
  • Microsoft SQL Server 2008 Standard
  • Microsoft SQL Server 2008 Enterprise
  • Microsoft SQL Server 2008 Developer
  • Microsoft SQL Server 2008 Workgroup
Keywords: 
kbsurveynew kbexpertiseadvanced kbqfe kbfix KB973877

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