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FIX: System performance may be slow when an application submits many queries against a SQL Server 2005 database that uses simple parameterizationArticle ID: 920206 - View products that this article applies to. 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. On This PageSUMMARYThis article describes the following about this hotfix release:
SYMPTOMSConsider 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. CAUSEThis 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. RESOLUTIONHotfix informationA 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: http://support.microsoft.com/contactus/?ws=support 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.
(http://support.microsoft.com/contactus/?ws=support)
PrerequisitesTo 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
(http://support.microsoft.com/kb/913089/
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How to obtain the latest service pack for SQL Server 2005
Restart informationYou do not have to restart the computer after you apply this hotfix.Registry informationYou do not have to change the registry.Hotfix replacement informationThis hotfix does not replace any other hotfixes.Hotfix file informationThis 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 Collapse this table
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STATUSMicrosoft has confirmed that this is a problem in the Microsoft products that are listed in the "Applies to" section. WORKAROUNDTo 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
(http://msdn2.microsoft.com/en-us/library/ms175580.aspx)
MORE INFORMATIONWhen 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
(http://support.microsoft.com/kb/824684/
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Description of the standard terminology that is used to describe Microsoft software updates
PropertiesArticle ID: 920206 - Last Review: September 17, 2011 - Revision: 2.0 APPLIES TO
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