Article ID: 247500 - View products that this article applies to.
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BUG #: 55597 (SQLBUG_70)
A query containing a sort operation may take significantly longer to execute using parallelism, as compared to being executed without parallelism. When the slow query is executing, sysprocesses shows a waittype of 0x208 or 0x200 and a lastwaittype of CXPACKET or EXCHANGE. This problem only affects a query executed against SQL Server running on a multi-processor server.
To determine whether a particular query encounters this condition, look at the plan and if you see a sort operation anywhere below the topmost parallelism step, this condition occurs. If you are using a graphical display of the plan such as the one generated by Query Analyzer, this would translate to a sort operation anywhere to the right of the left-most parallelism step.
For example, the following query demonstrates the problem:
Here is the summarized plan generated for this query:
Notice that the Sort operation occurs halfway down the plan, before the last Parallelism operator, which indicates that the sort will be performed in parallel.
|--Parallelism(Gather Streams) |--Nested Loops(Inner Join) |--Table Scan(OBJECT:(...)) |--Nested Loops(Inner Join) |--Merge Interval | |--Sort(ORDER BY:(...)) | |--Compute Scalar(DEFINE:(...)) | |--Concatenation | |--Compute Scalar(DEFINE:(...)) | | |--Constant Scan | |--Compute Scalar(DEFINE:(...)) | |--Constant Scan |--Index Seek(OBJECT:(...), SEEK:(...) ORDERED)
To work around this problem, add (MAXDOP 1) as a query hint. This hint overrides the max degree of parallelism configuration option (of sp_configure) only for the query specifying this option, and suppresses parallel plan generation. For more information on using this query hint, see the SELECT (T-SQL) topic in SQL Server 7.0 Books Online.
Microsoft has confirmed this to be a problem in SQL Server 7.0. This problem has been corrected in U.S. Service Pack 2 for Microsoft SQL Server 7.0. For more information, click the following article number to view the article in the Microsoft Knowledge Base:
254561For more information, contact your primary support provider.
(http://support.microsoft.com/kb/254561/ )INF: How to Obtain Service Pack 2 for Microsoft SQL Server 7.0 and Microsoft Data Engine (MSDE) 1.0
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