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.

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.

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: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: 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: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:

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: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: 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.

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

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.

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: 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: 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: 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: For more information about software update terminology, click the following article number to view the article in the Microsoft Knowledge Base: