FIX: A partitioned table may generate an inefficient query plan when you run a Transact-SQL query that uses the Top n clause on a partitioned table in SQL Server 2005

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Article ID: 924601 - View products that this article applies to.
Bug #:1253 (SQL Hotfix)
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.
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SUMMARY

This article describes the following about this hotfix release:
  • The issues that are fixed by this hotfix package
  • The prerequisites for applying the hotfix package
  • Whether you must restart the computer after you apply the hotfix package
  • Whether the hotfix package is replaced by any other hotfix package
  • Whether you must make any registry changes after you apply the hotfix package
  • The files that are contained in the hotfix package

SYMPTOMS

When you run a Transact-SQL query that uses the Top n clause on a partitioned table in Microsoft SQL Server 2005, the partitioned table may generate an inefficient query plan. The plan may perform a clustered index scan instead of performing a more efficient non-clustered index seek. For example, you experience this problem if the following conditions are true:
  • You run a query against a tblTest table. The query may resemble the following:
    SELECT top 1 * FROM tblTest WHERE OrderID = 'ABCDXYZ' ORDER BY OrderDateTime DESC
  • The tblTest table is partitioned on the OrderDateTime column.
  • A clustered index is created on the OrderDateTime column.
  • A non-clustered index is created on the OrderID column.
Notes
  • A clustered index scan is still performed without the use of the ORDER BY clause.
  • When the table and the indexes are not partitioned, a non-clustered index seek plan is generated.

CAUSE

This problem occurs because the query optimizer overestimates the cost of using an index seek with a partitioned table.

RESOLUTION

Hotfix information

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:
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.

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 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 x86 versions
Collapse this tableExpand this table
File nameFile versionFile sizeDateTimePlatform
Logread.exe2005.90.2187.0398,11231-Aug-200619:40x86
Microsoft.analysisservices.adomdclient.dll9.0.2187.0543,52031-Aug-200619:41x86
Microsoft.analysisservices.deploymentengine.dll9.0.2187.0138,01631-Aug-200619:38x86
Microsoft.analysisservices.dll9.0.2187.01,215,26431-Aug-200619:39x86
Microsoft.sqlserver.mgdsqldumper.dll2005.90.2187.075,55231-Aug-200619:37x86
Microsoft.sqlserver.sqlenum.dll9.0.2187.0908,06431-Aug-200619:39x86
Msgprox.dll2005.90.2187.0197,92031-Aug-200619:40x86
Msmdlocal.dll9.0.2187.015,610,14431-Aug-200619:39x86
Msmdredir.dll9.0.2187.03,990,30431-Aug-200619:40x86
Replprov.dll2005.90.2187.0547,61631-Aug-200619:41x86
Replrec.dll2005.90.2187.0782,11231-Aug-200619:39x86
Sqlaccess.dll2005.90.2187.0347,93631-Aug-200619:40x86
Sqlagent90.exe2005.90.2187.0319,26431-Aug-200619:39x86
Sqlservr.exe2005.90.2187.028,961,11231-Aug-200619:39x86
Xpstar90.dll2005.90.2187.0292,64031-Aug-200619:42x86
Xpstar90.rll2005.90.2187.0152,86431-Aug-200619:39x86
SQL Server 2005, 64-bit version
Collapse this tableExpand this table
File nameFile versionFile sizeDateTimePlatform
Logread.exe2005.90.2187.0522,52801-Sep-200600:06x64
Microsoft.analysisservices.adomdclient.dll9.0.2187.0543,52031-Aug-200619:41x86
Microsoft.analysisservices.adomdclient.dll9.0.2187.0543,52001-Sep-200600:02x86
Microsoft.analysisservices.deploymentengine.dll9.0.2187.0138,01631-Aug-200619:38x86
Microsoft.analysisservices.dll9.0.2187.01,215,26431-Aug-200619:39x86
Microsoft.sqlserver.mgdsqldumper.dll2005.90.2187.075,55231-Aug-200619:37x86
Microsoft.sqlserver.mgdsqldumper.dll2005.90.2187.091,42401-Sep-200600:03x64
Microsoft.sqlserver.sqlenum.dll9.0.2187.0875,29601-Sep-200600:04x86
Msgprox.dll2005.90.2187.0259,36001-Sep-200600:05x64
Msmdlocal.dll9.0.2187.015,610,14431-Aug-200619:39x86
Msmdredir.dll9.0.2187.03,990,30431-Aug-200619:40x86
Replprov.dll2005.90.2187.0745,24801-Sep-200600:03x64
Replrec.dll2005.90.2187.01,008,41601-Sep-200600:04x64
Sqlaccess.dll2005.90.2187.0355,10401-Sep-200600:06x86
Sqlagent90.exe2005.90.2187.0390,94401-Sep-200600:06x64
Sqlservr.exe2005.90.2187.039,341,85601-Sep-200600:03x64
Xpstar90.dll2005.90.2187.0540,96001-Sep-200600:06x64
Xpstar90.rll2005.90.2187.0153,37601-Sep-200600:04x64
SQL Server 2005, Itanium architecture version
Collapse this tableExpand this table
File nameFile versionFile sizeDateTimePlatform
Logread.exe2005.90.2187.01,095,45631-Aug-200623:02IA-64
Microsoft.analysisservices.adomdclient.dll9.0.2187.0543,52031-Aug-200619:41x86
Microsoft.analysisservices.adomdclient.dll9.0.2187.0543,52031-Aug-200623:01x86
Microsoft.analysisservices.deploymentengine.dll9.0.2187.0138,01631-Aug-200619:38x86
Microsoft.analysisservices.dll9.0.2187.01,215,26431-Aug-200619:39x86
Microsoft.sqlserver.mgdsqldumper.dll2005.90.2187.075,55231-Aug-200619:37x86
Microsoft.sqlserver.mgdsqldumper.dll2005.90.2187.0163,10431-Aug-200623:00IA-64
Microsoft.sqlserver.sqlenum.dll9.0.2187.0875,29631-Aug-200623:02x86
Msgprox.dll2005.90.2187.0542,49631-Aug-200623:01IA-64
Msmdlocal.dll9.0.2187.048,587,04031-Aug-200623:01IA-64
Msmdredir.dll9.0.2187.06,237,47231-Aug-200623:02IA-64
Replprov.dll2005.90.2187.01,617,18431-Aug-200623:02IA-64
Replrec.dll2005.90.2187.02,141,47231-Aug-200623:02IA-64
Sqlaccess.dll2005.90.2187.0349,47231-Aug-200623:01IA-64
Sqlagent90.exe2005.90.2187.01,143,58431-Aug-200623:02IA-64
Sqlservr.exe2005.90.2187.072,216,86431-Aug-200623:01IA-64
Xpstar90.dll2005.90.2187.0951,07231-Aug-200623:04IA-64
Xpstar90.rll2005.90.2187.0152,35231-Aug-200623:02IA-64

STATUS

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

MORE INFORMATION

For the query in the "Symptoms" section, a query plan that uses a partitioned table may resemble the following:
SELECT top 1 * FROM tblTest WHERE ORDERID = 'AE5PL-14' ORDER BY OrderDateTime DESC
|--Top(TOP EXPRESSION:((1)))
|--Nested Loops(Inner Join, OUTER REFERENCES:([PtnIds1004]) PARTITION ID:([PtnIds1004]))
|--Constant Scan(VALUES:(((32)),((31)),((30)),((29)),((28)),((27)),((26)),((25)),((24)),((23)),((22)),((21)),((20)),((19)),((18)),((17)),((16)),
((15)),((14)),((13)),((12)),((11)),((10)),((9)),((8)),((7)),((6)),((5)),((4)),((3)),((2)),((1))))
|--Clustered Index Scan(OBJECT:([part2].[dbo].[tblTest].[IX_tblTest_RT]), WHERE:([part2].[dbo].[tblTest].[OrderID]='AE5PL-14') 
ORDERED BACKWARD 
PARTITION ID:([PtnIds1004]))
A query plan that uses a non-partitioned table may resemble the following:
SELECT top 1 * FROM tblTest WHERE ORDERID = 'AE5PL-14' ORDER BY OrderDateTime DESC
|--Top(TOP EXPRESSION:((1)))
|--Nested Loops(Inner Join, OUTER REFERENCES:([Uniq1002], [nonpart2].[dbo].[tblTest].[OrderDateTime], [Expr1004]) WITH 
ORDERED PREFETCH)
|--Index Seek(OBJECT:([nonpart2].[dbo].[tblTest].[IX_tblTest]), SEEK:([nonpart2].[dbo].[tblTest].[OrderID]='AE5PL-14') ORDERED 
BACKWARD)
|--Clustered Index Seek(OBJECT:([nonpart2].[dbo].[tblTest].[IX_tblTest_RT]), SEEK:([nonpart2].[dbo].[tblTest].[OrderDateTime]=
[nonpart2].[dbo].[tblTest].[OrderDateTime] AND [Uniq1002]=[Uniq1002]) LOOKUP ORDERED FORWARD)

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

For more information about a related issue, click the following article number to view the article in the Microsoft Knowledge Base:
923849 FIX: When you run a query that references a partitioned table in SQL Server 2005, query performance may decrease

Properties

Article ID: 924601 - Last Review: October 9, 2011 - Revision: 2.0
APPLIES TO
  • Microsoft SQL Server 2005 Developer Edition
  • Microsoft SQL Server 2005 Enterprise Edition
  • Microsoft SQL Server 2005 Enterprise Edition for Itanium-based Systems
  • Microsoft SQL Server 2005 Enterprise X64 Edition
  • Microsoft SQL Server 2005 Standard X64 Edition
  • Microsoft SQL Server 2005 Standard Edition
Keywords: 
kbautohotfix kbfix kbexpertiseadvanced kbsql2005tsql kbHotfixServer kbqfe KB924601

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