FIX: Memory usage of the compiled query plan may unexpectedly increase in SQL Server 2005 (919636)


The information in this article 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
  • Microsoft SQL Server 2005 Enterprise Edition for Itanium Based Systems
  • Microsoft SQL Server 2005 Enterprise X64 Edition
  • SQL Server 2005 Standard Edition for Itanium-based Systems
  • Microsoft SQL Server 2005 Standard X64 Edition
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 "Value1", "Value2", "NewValue1", and "NewValue2" are ANSI strings. The values of the MyCol nvarchar column are first compared with the ANSI strings "Value1" and "Value2". Then, the corresponding value of the "NewValue1", "NewValue2" 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, but it is only intended to correct the problem that is described in this article. Only apply it to systems that are experiencing this specific problem. This hotfix may receive additional testing. Therefore, if you are not severely affected by this problem, we recommend that you wait for the next Microsoft SQL Server 2005 service pack that contains this hotfix.

To resolve this problem immediately, contact Microsoft Product Support Services to obtain the hotfix. For a complete list of Microsoft Product Support Services telephone numbers and information about support costs, visit the following Microsoft Web site:

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

Note In special cases, charges that are ordinarily incurred for support calls may be canceled if a Microsoft Support Professional determines that a specific update will resolve your problem. The usual support costs will apply to additional support questions and issues that do not qualify for the specific update in question.

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 "Workground" 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 32-bit version
File nameFile versionFile sizeDateTimePlatform
Microsoft.sqlserver.sqlenum.dll9.0.2164.0908,06414-Jun-200612:32x86
Microsoft.sqlserver.mgdsqldumper.dll2005.90.2164.075,55214-Jun-200612:29x86
Msgprox.dll2005.90.2164.0197,92014-Jun-200612:29x86
Replprov.dll2005.90.2164.0547,61614-Jun-200612:31x86
Replrec.dll2005.90.2164.0782,11214-Jun-200612:32x86
Msmdlocal.dll9.0.2164.015,661,85614-Jun-200612:33x86
Sqlaccess.dll2005.90.2164.0347,93614-Jun-200612:31x86
Sqlservr.exe2005.90.2164.028,950,87214-Jun-200612:33x86
SQL Server 2005 x64-based version
File nameFile versionFile sizeDateTimePlatform
Microsoft.sqlserver.sqlenum.dll9.0.2164.0875,29614-Jun-200613:12x86
Microsoft.sqlserver.mgdsqldumper.dll2005.90.2164.091,42414-Jun-200612:29x64
Msgprox.dll2005.90.2164.0259,36014-Jun-200613:10x64
Replprov.dll2005.90.2164.0745,24814-Jun-200613:12x64
Replrec.dll2005.90.2164.01,008,41614-Jun-200613:12x64
Msmdlocal.dll9.0.2164.015,661,85614-Jun-200612:33x86
Sqlaccess.dll2005.90.2164.0355,10414-Jun-200613:11x86
Sqlservr.exe2005.90.2164.039,251,23214-Jun-200613:13x64
SQL Server 2005 Itanium architecture version
File nameFile versionFile sizeDateTimePlatform
Microsoft.sqlserver.sqlenum.dll9.0.2164.0875,29614-Jun-200612:29x86
Microsoft.sqlserver.mgdsqldumper.dll2005.90.2164.0163,10414-Jun-200612:29IA-64
Msgprox.dll2005.90.2164.0542,49614-Jun-200612:28IA-64
Msmdlocal.dll9.0.2164.048,733,98414-Jun-200612:30IA-64
Replprov.dll2005.90.2164.01,617,18414-Jun-200612:29IA-64
Replrec.dll2005.90.2164.02,141,47214-Jun-200612:29IA-64
Sqlaccess.dll2005.90.2164.0349,47214-Jun-200612:28x86
Sqlservr.exe2005.90.2164.072,208,67214-Jun-200612:30IA-64

WORKAROUND

To work around this problem, add a uppercase letter "N" in front of all strings that are in the problem context. You can change the example that is described in the "Symptoms" 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 "Applies to" 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

Modification Type:MinorLast Reviewed:7/26/2006
Keywords:kbsql2005engine kbHotfixServer kbExpertiseAdvanced kbQFE kbfix kbpubtypekc KB919636 kbAudITPRO kbAudDeveloper
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