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Message Posted: Thu, 18 Jun 2015 @ 19:47:36 GMT


     
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Subj:   Re: Wrong Execution Plans
 
From:   Gregg, William

Hi -- U have come across one of the toughest things in our line of work. Staff use the stats diagnostic and apply all rec'd stats en masse. If the outcome is a good one, they move on. U have to take the time to id then apply only the useful stats. When that does not happen, your situation arises.

Another problem (fairly rare) is when a good stat goes bad. The only alert is when U receive a request to fix a query that has run without issue "since anyone can remember ..." In my case this is the last thing I consider investigating. Finding the bad stat in a large, complex qry is often time consuming.

The Optimizer does a great jobs these days, but it is not perfect.


Rgrds,

Bill Gregg
Teradata DBA



     
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