FIX: A query that you run by using a FORWARD_ONLY cursor takes a longer time to run in Microsoft SQL Server 2005 than in SQL Server 2000

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Article ID: 946793 - View products that this article applies to.
Bug: #50002254 (SQL Hotfix)
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

When you run a query by using a FORWARD_ONLY cursor in Microsoft SQL Server 2005, the query takes a long time to run. The same query runs faster in SQL Server 2000.

CAUSE

In SQL Server 2000, the execution plan for the query uses an Index Seek operator. In SQL Server 2005, the execution plan for the query uses an Index Scan operator. The optimizer produces an index spool for the Index Scan operation. When you use the FORWARD_ONLY cursor, SQL Server scans the index for every FETCH statement. Each fetch takes a long time. Therefore, the query takes a long time to execute.

RESOLUTION

The fix for this issue was first released in Cumulative Update 6. For more information about how to obtain this cumulative update package for SQL Server 2005 Service Pack 2, click the following article number to view the article in the Microsoft Knowledge Base:
946608 Cumulative update package 6 for SQL Server 2005 Service Pack 2
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:
937137 The SQL Server 2005 builds that were released after SQL Server 2005 Service Pack 2 was released
Microsoft SQL Server 2005 hotfixes are created for specific SQL Server service packs. You must apply a SQL Server 2005 Service Pack 2 hotfix to an installation of SQL Server 2005 Service Pack 2. By default, any hotfix that is provided in a SQL Server service pack is included in the next SQL Server service pack.

WORKAROUND

To work around this issue, use the OPTION (FAST 1) query hint for the query that is used in the cursor declaration or in the sp_cursoropen call.

STATUS

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

MORE INFORMATION

To resolve this issue by using this hotfix, enable trace flag 4115 after you apply the hotfix.

For more information about how to determine whether you are using a forward-only cursor in a cursor declaration, visit the following Microsoft Developer Network (MSDN) Web site:
http://msdn2.microsoft.com/en-us/library/ms180169.aspx
If you are using the sp_cursoropen stored procedure to open a cursor, you can specify the forward-only option in the third parameter of the sp_cursoropen stored procedure:
declare @p1 int
set @p1=0
declare @p3 int
set @p3=16388
declare @p4 int
set @p4=8194
declare @p5 int
set @p5=0
exec sp_cursoropen @p1 output, <Transact-SQL statement> ,@p3 output,@p4 output,@p5 output
Note In the sample code, the third parameter "16388" represents 16384 (the AutoClose option) + 4 (the forward-only option). The fourth parameter "8194" represents 8192 (the Allow_direct option) + 2 (the Scroll_Locks option).

For more information about what files are changed, and for information about any prerequisites to apply the cumulative update package that contains the hotfix that is described in this Microsoft Knowledge Base article, click the following article number to view the article in the Microsoft Knowledge Base:
946608 Cumulative update package 6 for SQL Server 2005 Service Pack 2

REFERENCES

For more information about the list of builds that are available after SQL Server Service Pack 2, click the following article number to view the article in the Microsoft Knowledge Base:
937137 The SQL Server 2005 builds that were released after SQL Server 2005 Service Pack 2 was released
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 2, 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 and the improvements in SQL Server 2005 Service Pack 2, visit the following Microsoft Web site:
http://go.microsoft.com/fwlink/?LinkId=71711
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: 946793 - Last Review: February 5, 2008 - Revision: 1.1
APPLIES TO
  • Microsoft SQL Server 2005 Standard Edition
  • Microsoft SQL Server 2005 Developer Edition
  • Microsoft SQL Server 2005 Enterprise Edition
  • Microsoft SQL Server 2005 Standard X64 Edition
  • Microsoft SQL Server 2005 Standard Edition for Itanium-based Systems
  • Microsoft SQL Server 2005 Enterprise X64 Edition
  • Microsoft SQL Server 2005 Enterprise Edition for Itanium-based Systems
Keywords: 
kbsql2005engine kbhotfixrollup kbfix kbpubtypekc kbqfe kbexpertiseadvanced KB946793

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