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

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Article ID: 266372 - View products that this article applies to.
This article was previously published under Q266372
BUG #: 58092 (SQLBUG_70)
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A complex UPDATE statement using the OPTION (MAXDOP 1) hint on multiprocessor computers may not turn off parallel query plan.


To turn off parallelism, do one of the following:
  • Run the following code:
    sp_configure 'max degree of parallelism', 1
    reconfigure with override

  • 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.


For more information, contact your primary support provider.


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
  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


Article ID: 266372 - Last Review: March 14, 2006 - Revision: 2.1
  • Microsoft SQL Server 7.0 Standard Edition
kbbug kbfix KB266372

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