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

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

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: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.

A supported hotfix is 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 software update that contains this hotfix.

If the hotfix is available for download, there is a "Hotfix download available" section at the top of this Knowledge Base article. If this section does not appear, contact Microsoft Customer Service and Support to obtain the hotfix.

Note If additional issues occur or if 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. For a complete list of Microsoft Customer Service and Support telephone numbers or to create a separate service request, visit the following Microsoft Web site: Note The "Hotfix download available" form displays the languages for which the hotfix is available. If you do not see your language, it is because a hotfix is not available for that language.

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:

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

SQL Server 2005 x64-based version

SQL Server 2005 Itanium architecture version

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:

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

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: For more information about the sys.dm_exec_cached_plans dynamic management view, visit the following MSDN Web site: 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: For more information about software update terminology, click the following article number to view the article in the Microsoft Knowledge Base: