From: Tom Lane <tgl@sss.pgh.pa.us>
To: Midge Brown <midgems@sbcglobal.net>
Cc: pgsql-performance@postgresql.org
Subject: Re: slow query, different plans
Date: Sat, 04 Aug 2012 02:26:42 -0400
Message-ID: <25289.1344061602@sss.pgh.pa.us> (raw)
In-Reply-To: <9CF5A680782142D794A085320949FED4@BERNICE>
References: <9CF5A680782142D794A085320949FED4@BERNICE>
"Midge Brown" <midgems@sbcglobal.net> writes:
> I'm having a problem with a query on our production server, but not on a laptop running a similar postgres version with a recent backup copy of the same table. I tried reindexing the table on the production server, but it didn't make any difference. Other queries on the same table are plenty fast.
Reindexing won't help that. The problem is a bad statistical estimate;
it thinks there are about 700 rows with applies2 = 256, when there's
really only one. That means the "fast" plan is a lot faster than the
planner gives it credit for, and conversely the "slow" plan is a lot
slower than the planner is expecting. Their estimated costs end up
nearly the same, which makes it a bit of a chance matter which one is
picked --- but the true costs are a lot different. So you need to fix
that rowcount estimate. Raising the stats target for the table might
help.
regards, tom lane
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To: pgsql-performance@postgresql.org
Cc: tgl@sss.pgh.pa.us, midgems@sbcglobal.net
Subject: Re: slow query, different plans
In-Reply-To: <25289.1344061602@sss.pgh.pa.us>
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