Re: *_collapse_limit, geqo_threshold - Mailing list pgsql-hackers

From Kevin Grittner
Subject Re: *_collapse_limit, geqo_threshold
Date
Msg-id 4A54C59702000025000285E8@gw.wicourts.gov
Whole thread Raw
In response to Re: *_collapse_limit, geqo_threshold  (Tom Lane <tgl@sss.pgh.pa.us>)
Responses Re: *_collapse_limit, geqo_threshold
Re: *_collapse_limit, geqo_threshold
List pgsql-hackers
Tom Lane <tgl@sss.pgh.pa.us> wrote: 
> It occurs to me that one way to make GEQO less scary would be to
> take out the nondeterminism by resetting its random number generator
> for each query.  You might get a good plan or an awful one, but at
> least it'd be the same one each time.  DBAs like predictability.
+1  The biggest reason that I've tended to avoid geqo is that I would
never know when it might do something really stupid with a query one
time out of some large number, leading to mysterious complaints which
could eat a lot of time.
For a moment it seemed logical to suggest a session GUC for the seed,
so if you got a bad plan you could keep rolling the dice until you got
one you liked; but my right-brain kept sending shivers down my spine
to suggest just how uncomfortable it was with that idea....
-Kevin


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