October 21, 2010 at 6:56 am
Hi ,
Just come across an interest case while investigating an SP.
The query plan shows parallelism even though the run time is 0.2 seconds. The server setting for MAXDOP is 0 and the
cost threshold for parallelism is at 5 seconds.
I ran the query with Maxdrop option 1 and the duration remains the similar while cpu usage is halved.
Sorry if I may have rambled a bit but my question is..
Why if the execution time is well under 5 seconds is the optimizer/engine bringing parallelism to the query?
Regards
Eoin
PS I know that according to the rules of etiquette, I should post the SP code, however this is more of an engine/optimizer decision query.
October 22, 2010 at 2:51 am
Bump
October 22, 2010 at 3:36 am
From http://technet.microsoft.com/en-us/library/ms188603(SQL.90).aspx:
In certain cases, a parallel plan may be chosen even though the query's cost plan is less than the current cost threshold for parallelism value. This can happen because the decision to use a parallel or serial plan is based on a cost estimate provided before the full optimization is complete.
Looks like you're running into one of these cases based on the query.
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