Microsoft KB Archive/943060

= FIX: A query that has many outer joins takes a long time to compile in SQL Server 2005 =

Article ID: 943060

Article Last Modified on 11/20/2007

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APPLIES TO


 * Microsoft SQL Server 2005 Standard Edition
 * Microsoft SQL Server 2005 Developer Edition
 * 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 Standard X64 Edition
 * Microsoft SQL Server 2005 Standard Edition for Itanium-based Systems

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Bug #: 50001887 (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.



SYMPTOMS
In Microsoft SQL Server 2005, you run a query that has many outer joins. When you do this, the query takes a long time to compile. Additionally, error messages that resemble the following are logged in the SQL Server error log:

Server ***Unable to get thread context - no pss

Server * *******************************************************************************

Server *

Server * BEGIN STACK DUMP:

Server *   spid 0

Server *

Server * Non-yielding Scheduler

Server *

Server * *******************************************************************************

Server Stack Signature for the dump is 0x00000000000000DB

Server External dump process return code 0x20002001. The error information has been submitted to Watson error reporting.

Server Process 63:0:0 (0x175c) Worker 0x000000008A35A1C0 appears to be non-yielding on Scheduler 0. Thread creation time: 12834554418123. Approx Thread CPU Used: kernel 62 ms, user 68000 ms. Process Utilization 48%. System Idle 45%. Interval: 70013 ms.

……

When this issue occurs, a minidump file is generated.

Note This issue does not occur if you run the same query in Microsoft SQL Server 2000.



CAUSE
This issue occurs because SQL Server 2005 takes a long time to recursively check the plan nodes for parallel operations when SQL Server 2005 generates an execution plan for the query.



RESOLUTION
The fix for this issue was first released in Cumulative Update 4. For more information about how to obtain this cumulative update package for SQL Server 2005 Service Pack 2, click the following article number to view the article in the Microsoft Knowledge Base:

941450 Cumulative update package 4 for SQL Server 2005 Service Pack 2

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 2005 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:

937137 The SQL Server 2005 builds that were released after SQL Server 2005 Service Pack 2 was released

Microsoft SQL Server 2005 hotfixes are created for specific SQL Server service packs. You must apply a SQL Server 2005 Service Pack 2 hotfix to an installation of SQL Server 2005 Service Pack 2. By default, any hotfix that is provided in a SQL Server service pack is included in the next SQL Server service pack.



WORKAROUND
To work around this issue, set the MAXDOP query hint to 1 for the query.



STATUS
Microsoft has confirmed that this is a problem in the Microsoft products that are listed in the &quot;Applies to&quot; section.



MORE INFORMATION
After you apply this cumulative update package, you must enable trace flag 4123 to fix this issue. When trace flag 4123 is enabled, SQL Server 2005 disables a query optimizer transformation that is required to implement a full outer join by using a loop join. Therefore, you may receive the following error message in rare cases:

Server: Msg 8622, Level 16, State 1, Line 1

Query processor could not produce a query plan because of the hints defined in this query. Resubmit the query without specifying any hints and without using SET FORCEPLAN.

You receive this error message if you explicitly use the LOOP JOIN query hint for the full outer join in the query.

For more information about what files are changed, and for information about any prerequisites to apply the cumulative update package that contains the hotfix that is described in this Microsoft Knowledge Base article, click the following article number to view the article in the Microsoft Knowledge Base:

941450 Cumulative update package 4 for SQL Server 2005 Service Pack 2

