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Article ID: 973255 - Last Review: September 22, 2009 - Revision: 1.1

Microsoft distributes Microsoft SQL Server 2008 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 2008 fix release.

SYMPTOMS

In Microsoft SQL Server 2008, you create a partitioned view. You run a query that uses the MIN or MAX aggregate function against the partitioned view. However, you may find the query runs much slower in SQL Server 2008 than if you run the same query in SQL Server 2005.

If you examine the execution plan of the query, you find that the TOP operator presents in the execution plan in SQL Server 2005. However, the TOP operator does not present in the execution plan in SQL Server 2008.

For example, the execution plan in SQL Server 2005 resembles the following:
  |--Stream Aggregate(DEFINE:([Expr1190]=MAX([partialagg1191])))
       |--Concatenation
            |--Top(TOP EXPRESSION:((1)))
            |    |--Clustered Index Scan(OBJECT:([Server].[dbo].[Database].[PK]), ORDERED BACKWARD)
            |--Top(TOP EXPRESSION:((1)))
                 |--Clustered Index Scan(OBJECT:([Server].[dbo].[Database].[PK]), ORDERED BACKWARD)
However, the execution plan of the same query in SQL Server 2008 resembles the following:
  |--Stream Aggregate(DEFINE:([Expr1190]=MAX([partialagg1191])))
       |--Concatenation
            |--Stream Aggregate(DEFINE:([partialagg1191]=MAX([Server].[dbo].[Database].[Column])))
            |    |--Index Scan(OBJECT:([Server].[dbo].[Database].[Index]))
            |--Stream Aggregate(DEFINE:([partialagg1191]=MAX([Server].[dbo].[Database].[Column])))
                 |--Index Scan(OBJECT:([Server].[dbo].[Database].[Index]))

CAUSE

The SQL Database Engine introduces a rule that translates the MIN and MAX aggregation functions to use TOP (1) operator and the Index Seek operator on the execution plan. However, in this scenario, the rule does not work in SQL Server 2008. Therefore, a wrong index is used on the partition view. This causes the performance issue.

RESOLUTION

The fix for this issue was first released in Cumulative Update 4 for SQL Server 2008 Service Pack 1. For more information about this cumulative update package, click the following article number to view the article in the Microsoft Knowledge Base:
973602  (http://support.microsoft.com/kb/973602/LN/ ) Cumulative update package 4 for SQL Server 2008 Service Pack 1
Note Because the builds are cumulative, each new fix release contains all the hotfixes and all the security fixes that were included with the previous SQL Server 2008 fix release. Microsoft recommends that you consider applying the most recent fix release that contains this hotfix. For more information, click the following article number to view the article in the Microsoft Knowledge Base:
970365  (http://support.microsoft.com/kb/970365/LN/ ) The SQL Server 2008 builds that were released after SQL Server 2008 Service Pack 1 was released
Microsoft SQL Server 2008 hotfixes are created for specific SQL Server service packs. You must apply a SQL Server 2008 Service Pack 1 hotfix to an installation of SQL Server 2008 Service Pack 1. By default, any hotfix that is provided in a SQL Server service pack is included in the next SQL Server service pack.
You must enable trace flag 4199 for this hotfix to take effect.

STATUS

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

REFERENCES

For more information about the Incremental Servicing Model for SQL Server, click the following article number to view the article in the Microsoft Knowledge Base:
935897  (http://support.microsoft.com/kb/935897/ ) An Incremental Servicing Model is available from the SQL Server team to deliver hotfixes for reported problems


For more information about the naming schema for SQL Server updates, click the following article number to view the article in the Microsoft Knowledge Base:
822499  (http://support.microsoft.com/kb/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  (http://support.microsoft.com/kb/824684/ ) Description of the standard terminology that is used to describe Microsoft software updates

APPLIES TO
  • Microsoft SQL Server 2008 Standard
  • Microsoft SQL Server 2008 Developer
  • Microsoft SQL Server 2008 Enterprise
  • Microsoft SQL Server 2008 Workgroup
Keywords: 
kbsurveynew kbfix kbqfe kbexpertiseadvanced KB973255
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