FIX: OPTION (MAXDOP 1) Hint May Not Turn Off Parallel Query

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This article was previously published under Q266372

BUG #: 58092 (SQLBUG_70)

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SYMPTOMS

A complex UPDATE statement using the OPTION (MAXDOP 1) hint on multiprocessor computers may not turn off parallel query plan.

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WORKAROUND

To turn off parallelism, do one of the following:

Run the following code:

sp_configure 'max degree of parallelism', 1
go
reconfigure with override

-or-

Increase 'cost threshold for parallelism' in sp_configure to reduce the chance of a parallel query plan being chosen for the query. One would have to test and find the minimum value for this setting on your computer to avoid a parallel plan for the query because it is related to both the query and the data in the tables involved in the query.

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Microsoft has confirmed this to be a problem in SQL Server 7.0. This problem has been corrected in U.S. Service Pack 3 for Microsoft SQL Server 7.0. For more information, click the following article number to view the article in the Microsoft Knowledge Base:

274799 (http://support.microsoft.com/kb/274799/ ) INF: How to Obtain Service Pack 3 for Microsoft SQL Server 7.0 and Microsoft Data Engine (MSDE) 1.0

For more information, contact your primary support provider.

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MORE INFORMATION

The following is an example of the complex UPDATE query reported in this bug:

UPDATE  tab_x SET 
  c1 = tab0.a,
  c2 = tab1.a,
  c3 = tab2.a,
  c4 = tab3.a,
  c5 = tab4.a,
  c6 = tab5.a,
  c7 = tab6.a,
  c8 = tab7.a
FROM 
  tab_y INNER JOIN tab_x ON tab_y.b1 = tab_x.c9 
  LEFT OUTER JOIN tab7 ON tab_y.b2 = tab7.b2 
  LEFT OUTER JOIN tab6 ON tab_y.b3 = tab6.b2
  LEFT OUTER JOIN tab5 ON tab_y.b4 = tab5.b2 
  LEFT OUTER JOIN tab4 ON tab_y.b5 = tab4.b2
  LEFT OUTER JOIN tab3 ON tab_y.b6 = tab3.b2 
  LEFT OUTER JOIN tab2 ON tab_y.b7 = tab2.b2 
  LEFT OUTER JOIN tab1 ON tab_y.b8 = tab1.b2 
  LEFT OUTER JOIN tab0 ON tab_y.b9 = tab0.b2

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