From: | Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> |
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To: | Thomas Munro <thomas(dot)munro(at)enterprisedb(dot)com> |
Cc: | Jeff Janes <jeff(dot)janes(at)gmail(dot)com>, pgsql-hackers <pgsql-hackers(at)postgresql(dot)org> |
Subject: | Re: neqjoinsel versus "refresh materialized view concurrently" |
Date: | 2018-03-13 23:29:38 |
Message-ID: | 9724.1520983778@sss.pgh.pa.us |
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Lists: | pgsql-hackers |
Thomas Munro <thomas(dot)munro(at)enterprisedb(dot)com> writes:
> There is a fundamental and complicated estimation problem lurking here
> of course and I'm not sure what to think about that yet. Maybe there
> is a very simple fix for this particular problem:
Ah, I see you thought of the same hack I did.
I think this may actually be a good fix, and here's the reason: this plan
is in fact being driven entirely off planner default estimates, because
we don't have any estimation code that knows what to do with
"wholerowvar *= wholerowvar". I'm suspicious that we could drop the
preceding ANALYZE as being a waste of cycles, except maybe it's finding
out the number of rows for us. In any case, LIMIT 1 is only a good idea
to the extent that the planner knows what it's doing, and this is an
example where it demonstrably doesn't and won't any time soon.
regards, tom lane
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