From: Tom Lane <tgl@sss.pgh.pa.us>
To: Csaba Nagy <nagy@ecircle-ag.com>
Cc: postgres performance list <pgsql-performance@postgresql.org>
Subject: Re: Searching for the cause of a bad plan
Date: Fri, 21 Sep 2007 12:08:33 -0400
Message-ID: <6175.1190390913@sss.pgh.pa.us> (raw)
In-Reply-To: <1190369024.4661.173.camel@PCD12478>
References: <1190369024.4661.173.camel@PCD12478>
Csaba Nagy <nagy@ecircle-ag.com> writes:
> Looking at Plan 2, it looks like the "limit" step is estimating wrongly
> it's cost.
The reason you get a bad plan is that this rowcount estimate is so far
off:
> -> Index Scan using pk_table_a on table_a ta (cost=0.00..324786.18 rows=388532 width=16) (actual time=454.389..460.138 rows=2 loops=1)
> Index Cond: (a = $1)
Raising the stats target helped no doubt because it didn't overestimate
the number of rows so much...
regards, tom lane
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Subject: Re: Searching for the cause of a bad plan
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