August 19, 2015 at 5:54 am
I often use profiler as one tool to help identify bad plans. The reads column gives me a good indication of excessive IO to dig into and correct if necessary. I often use it with Showplan so I can see what a query does, replicate it and fix it.
However I have just lost some faith in it. I am looking at a poorly performing query joining five tables. A parallel plan has been generated and one table is being scanned (in parallel) due to a missing index. This table had in excess of 4 million rows in it. The rest hitd indexes well. However the entire query generates ONLY 12 READS.
Once corrected, a single processor plan is used. This looks really efficient and uses 120 reads. That looks the right figure to me.
Clearly 12 reads is wrong. Can anyone shed any light on this? Does the profiler only display one thread of a parallel plan perhaps? Or something else?
I'm a bit worried now that I can't trust some of he statistics I base my decisions on.
(I do use a number of other techniques, such as DMVs, too)
Thanks
Tim
Edit - DMV, not DMC ! Its a dynamic management view not a rap trio!
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August 19, 2015 at 6:05 am
SORRY misposted this
Have reposted under SQL 2012 - General
Please reply there
Apologies
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