Microsoft KB Archive/919636

= FIX: Memory usage of the compiled query plan may unexpectedly increase in SQL Server 2005 =

Article ID: 919636

Article Last Modified on 11/20/2007

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APPLIES TO


 * Microsoft SQL Server 2005 Standard Edition
 * Microsoft SQL Server 2005 Developer Edition
 * Microsoft SQL Server 2005 Enterprise Edition
 * Microsoft SQL Server 2005 Workgroup Edition
 * Microsoft SQL Server 2005 Enterprise Edition for Itanium-based Systems
 * Microsoft SQL Server 2005 Enterprise X64 Edition
 * Microsoft SQL Server 2005 Standard Edition for Itanium-based Systems
 * Microsoft SQL Server 2005 Standard X64 Edition

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Bug #: 810 (SQL Hotfix)



Notice
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.



This article describes the following about this hotfix release:
 * The issues that are fixed by this hotfix package
 * The prerequisites for installing the hotfix package
 * Information about whether you must restart the computer after you install the hotfix package
 * Information about whether the hotfix package is replaced by any other hotfix package
 * Information about whether you must make any registry changes
 * The files that are contained in the hotfix package



SYMPTOMS
When you examine the compiled query plan of a query, you may notice that the memory usage of the complied query plan may unexpectedly increase in SQL Server 2005 compared to Microsoft SQL Server 2000.

This problem may occur when one of the following conditions is true:
 * Condition 1: The query references a table that uses computed columns.
 * Condition 2: The query contains string operations between the values of nvarchar columns and ANSI strings. For example, the string operation compares the values of nvarchar columns to ANSI strings.
 * Condition 3: The query contains a reference to a table that has a computed column. The computed column is based on an nvarchar column. However, the computer column uses ANSI string constants in the expression.

Conditions 2 and 3 can cause a significant increase in the memory usage of a compiled query plan.

For example, you have a table that has an nvarchar column. The table name is MyTable, and the nvarchar column name is MyCol. Then, you define the query by using the following syntax: SELECT CASE MyCol WHEN 'Value1' THEN 'NewValue1' WHEN 'Value2' THEN 'NewValue2' ELSE MyCol END FROM MyTable In this example, the strings &quot;Value1&quot;, &quot;Value2&quot;, &quot;NewValue1&quot;, and &quot;NewValue2&quot; are ANSI strings. The values of the MyCol nvarchar column are first compared with the ANSI strings &quot;Value1&quot; and &quot;Value2&quot;. Then, the corresponding value of the &quot;NewValue1&quot;, &quot;NewValue2&quot; ANSI string or the original value of the MyCol column is chosen.

You can view the compiled plan memory usage by examining the pagesused column of the sys.syscacheobjects system table or the sys.dm_exec_cached_plans dynamic management view.

This increased size of the complied query plan can also lead to a wait time increase for the RESOURCE_SEMAPHORE_QUERY_COMPILE wait type.



RESOLUTION
A supported hotfix is now available from Microsoft. However, this hotfix is intended to correct only the problem that is described in this article. Apply this hotfix only to systems that are experiencing this specific problem. This hotfix might receive additional testing. Therefore, if you are not severely affected by this problem, we recommend that you wait for the next service pack that contains this hotfix.

To resolve this problem, submit a request to Microsoft Online Customer Services to obtain the hotfix. To submit an online request to obtain the hotfix, visit the following Microsoft Web site:

http://go.microsoft.com/?linkid=6294451

Note If additional issues occur or any troubleshooting is required, you might have to create a separate service request. The usual support costs will apply to additional support questions and issues that do not qualify for this specific hotfix. To create a separate service request, visit the following Microsoft Web site:

http://support.microsoft.com/contactus/?ws=support

Prerequisites
You must have SQL Server 2005 Service Pack 1 (SP1) installed to apply this hotfix. For more information about how to obtain SQL Server 2005 Service Pack 1, 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

Restart information
You do not have to restart the computer after you apply this hotfix. However, if you have already affected by this problem, you must follow the steps in the &quot;Workground&quot; section after you apply this hotfix to revert the database files to a healthy state.

Registry information
You do not have to change the registry.

Hotfix file information
This hotfix contains only those files that are required to correct the issues that this article lists. This hotfix may not contain of all the files that you must have to fully update a product to the latest build.

The English version of this hotfix has the file attributes (or later file attributes) that are listed in the following table. The dates and times for these files are listed in Coordinated Universal Time (UTC). When you view the file information, it is converted to local time. To find the difference between UTC and local time, use the Time Zone tab in the Date and Time item in Control Panel.

SQL Server 2005 Itanium architecture version


WORKAROUND
To work around this problem, add a uppercase letter &quot;N&quot; in front of all strings that are in the problem context. You can change the example that is described in the &quot;Symptoms&quot; section by using the following syntax: SELECT CASE MyCol WHEN N'Value1' THEN N'NewValue1' WHEN N'Value2' THEN N'NewValue2' ELSE MyCol END FROM MyTable



STATUS
Microsoft has confirmed that this is a problem in the Microsoft products that are listed in the &quot;Applies to&quot; section.



MORE INFORMATION
You can view the compiled plan memory usage by examining the pagesused column of the sys.syscacheobjects system table or the sys.dm_exec_cached_plans dynamic management view.

For more information about the sys.syscacheobjects system table, visit the following Microsoft Developer Network (MSDN) Web site:

http://msdn2.microsoft.com/en-us/library/ms187815.aspx

For more information about the sys.dm_exec_cached_plans dynamic management view, visit the following MSDN Web site:

http://msdn2.microsoft.com/en-us/library/ms187404.aspx

For more information about the naming schema for Microsoft 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

Keywords: kbfix kbqfe kbpubtypekc kbexpertiseadvanced kbhotfixserver kbsql2005engine KB919636

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