FIX: System performance may be slow when an application submits many queries against a SQL Server 2005 database that uses simple parameterization (920206)


The information in this article applies to:

  • Microsoft SQL Server 2005 Standard Edition
  • Microsoft SQL Server 2005 Standard X64 Edition
  • SQL Server 2005 Standard Edition for Itanium-based Systems
  • Microsoft SQL Server 2005 Enterprise Edition
  • Microsoft SQL Server 2005 Enterprise X64 Edition
  • Microsoft SQL Server 2005 Enterprise Edition for Itanium Based Systems
  • Microsoft SQL Server 2005 Developer Edition
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.

SUMMARY

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
  • Whether you must restart the computer after you install the hotfix package
  • Whether the hotfix package is replaced by any other hotfix package
  • Whether you must make any registry changes
  • The files that are contained in the hotfix package

SYMPTOMS

Consider the following scenario: An application submits many queries against a Microsoft SQL Server 2005 database. The queries have identical query text and declare the same parameters. However, the queries also have different combinations of precision and scale for the values of the numeric data type in the parameter declaration string. The SQL Server 2005 database uses simple parameterization. In this scenario, SQL Server 2005 system performance may be slow. Additionally, you may experience high CPU usage.

This problem occurs more frequently when the SQL Server 2005 database is large and is in a high-stress scenario.

Note The default behavior of a SQL Server 2005 database is to use simple parameterization.

CAUSE

This problem occurs because SQL Server must examine many queries to find the one query that is a match to the query text, the parameters, and the parameter declaration string.

RESOLUTION

Hotfix information

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 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

To apply this hotfix, you must have SQL Server 2005 Service Pack 1 (SP1) installed on the computer.
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.

Registry information

You do not have to change the registry.

Hotfix replacement information

This hotfix does not replace any other hotfixes.

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 hotfix, 32-bit
File nameFile versionFile sizeDateTimePlatform
Microsoft.sqlserver.mgdsqldumper.dll2005.90.2164.075,55214-Jun-200620:29x86
Microsoft.sqlserver.sqlenum.dll9.0.2164.0908,06414-Jun-200620:32x86
Msgprox.dll2005.90.2164.0197,92014-Jun-200620:29x86
Msmdlocal.dll9.0.2164.015,661,85614-Jun-200620:33x86
Mssqlsystemresource.ldfNot applicable524,28814-Jun-200614:23Not applicable
Mssqlsystemresource.mdfNot applicable39,911,42414-Jun-200614:23Not applicable
Replprov.dll2005.90.2164.0547,61614-Jun-200620:31x86
Replrec.dll2005.90.2164.0782,11214-Jun-200620:32x86
Sqlaccess.dll2005.90.2164.0347,93614-Jun-200620:31x86
Sqlservr.exe2005.90.2164.028,950,87214-Jun-200620:33x86
SQL Server 2005 hotfix, 64-bit
File nameFile versionFile sizeDateTimePlatform
Microsoft.sqlserver.mgdsqldumper.dll2005.90.2164.075,55214-Jun-200620:29x86
Microsoft.sqlserver.mgdsqldumper.dll2005.90.2164.091,42414-Jun-200621:10x64
Microsoft.sqlserver.sqlenum.dll9.0.2164.0875,29614-Jun-200621:12x86
Msgprox.dll2005.90.2164.0259,36014-Jun-200621:10x64
Msmdlocal.dll9.0.2164.015,661,85614-Jun-200620:33x86
Mssqlsystemresource.ldfNot applicable524,28814-Jun-200614:23Not applicable
Mssqlsystemresource.mdfNot applicable39,911,42414-Jun-200614:23Not applicable
Replprov.dll2005.90.2164.0745,24814-Jun-200621:12x64
Replrec.dll2005.90.2164.01,008,41614-Jun-200621:12x64
Sqlaccess.dll2005.90.2164.0355,10414-Jun-200621:11x86
Sqlservr.exe2005.90.2164.039,251,23214-Jun-200621:13x64
SQL Server 2005 hotfix, 64-bit for Itanium processors
File nameFile versionFile sizeDateTimePlatform
Microsoft.sqlserver.mgdsqldumper.dll2005.90.2164.0163,10414-Jun-200620:29IA-64
Microsoft.sqlserver.mgdsqldumper.dll2005.90.2164.075,55214-Jun-200620:29x86
Microsoft.sqlserver.sqlenum.dll9.0.2164.0875,29614-Jun-200620:29x86
Msgprox.dll2005.90.2164.0542,49614-Jun-200620:28IA-64
Msmdlocal.dll9.0.2164.048,733,98414-Jun-200620:30IA-64
Mssqlsystemresource.ldfNot applicable524,28814-Jun-200614:23Not applicable
Mssqlsystemresource.mdfNot applicable39,911,42414-Jun-200614:23Not applicable
Replprov.dll2005.90.2164.01,617,18414-Jun-200620:29IA-64
Replrec.dll2005.90.2164.02,141,47214-Jun-200620:29IA-64
Sqlaccess.dll2005.90.2164.0349,47214-Jun-200620:28x86
Sqlservr.exe2005.90.2164.072,208,67214-Jun-200620:30IA-64

STATUS

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

WORKAROUND

To work around this problem, use explicit parameterization in the client application. When you use explicit parameterization in the client application, only one execution plan is created and stored in the procedure cache. In this workaround, SQL Server 2005 system performance runs as expected.

For more information about explicit parameterization and execution plan reuse, visit the following Microsoft Developer Network (MSDN) Web site:

http://msdn2.microsoft.com/en-us/library/ms175580.aspx

MORE INFORMATION

When an application submits many queries against a SQL Server 2005 database, the execution plan for each query must be present in the procedure cache before the query can be executed.

Note If the execution plan for a specific query is not present in the procedure cache, SQL Server compiles the query, writes the execution plan for the query to the procedure cache, and then executes the query.

When SQL Server 2005 retrieves a cached execution plan for a specific query from the procedure cache, SQL Server identifies the corresponding execution plan by using a hash key that was derived when the query was compiled. The original release version of SQL Server 2005 derives hash keys from the query text only and skips the parameter declaration string. When SQL Server 2005 derives hash keys from the query text only, SQL Server 2005 puts the hash keys for all queries that have identical query text and the same parameters in the same hash bucket. This behavior occurs even if each query has a different combination of precision and scale for the numeric values in the parameter declaration string. When SQL Server 2005 tries to retrieve a cached query execution plan from the procedure cache for a specific query, SQL Server must examine all the query execution plans in the matching hash bucket to find the one query execution plan that matches the query text, the parameters, and the parameter declaration string.

After you apply this hotfix, SQL Server 2005 derives hash keys from the query text and the parameter declaration string. When a new query has a combination of precision and scale for the numeric values in the parameter declaration string that does not match another existing query, SQL Server 2005 puts the hash key for the new query in a new hash bucket. SQL Server 2005 puts the hash key for the new query in a new hash bucket even when the new query has identical query text and the same parameters as another existing query. Therefore, when SQL Server 2005 tries to retrieve the cached execution plans from the procedure cache for the new query, the matching hash bucket contains only one query for SQL Server to examine.

In this hotfix resolution scenario, SQL Server 2005 still has many execution plans. This occurs because a separate execution plan is created for each query that has a new combination of precision and scale for the numeric values in the parameter declaration string. Each execution plan requires SQL Server 2005 system resources to create the execution plan. Each execution plan requires SQL Server 2005 system resources to store the execution plan in the procedure cache. Because the hotfix resolution scenario requires lots of SQL Server 2005 system resources, SQL Server 2005 system performance may still be slower than expected.
For more information, 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:MajorLast Reviewed:9/26/2006
Keywords:kbBug kbfix kbtshoot kbQFE kbhotfixserver kbpubtypekc KB920206 kbAudITPRO kbAudDeveloper
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