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Re: Wrong index choosen?

From: Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>
To: Dennis Bjorklund <db(at)zigo(dot)dhs(dot)org>
Cc: Gaetano Mendola <mendola(at)bigfoot(dot)com>,"pgsql-hackers(at)postgresql(dot)org" <pgsql-hackers(at)postgresql(dot)org>
Subject: Re: Wrong index choosen?
Date: 2004-07-23 14:45:27
Message-ID: (view raw, whole thread or download thread mbox)
Lists: pgsql-hackerspgsql-performance
Dennis Bjorklund <db(at)zigo(dot)dhs(dot)org> writes:
> In this plan it estimates to get 481 but it got 22477. So the estimation 
> was very wrong. You can increase the statistics tarhet on the login_time 
> and it will probably be better (after the next analyze).

Given the nature of the data (login times), I'd imagine that the problem
is simply that he hasn't analyzed recently enough.  A bump in stats
target may not be needed, but he's going to have to re-analyze that
column often if he wants this sort of query to be estimated accurately,
because the fraction of entries later than a given time T is *always*
going to be changing.

			regards, tom lane

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