Re: Forcing the right queryplan

On Thu, Sep 09, 2010 at 10:50:52AM -0400, Tom Lane wrote:
> Henk van Lingen <H(dot)G(dot)K(dot)vanLingen(at)uu(dot)nl> writes:
> > -> Bitmap Heap Scan on systemevents (cost=61221.23..668806.93 rows=239805 width=158) (actual time=9.131..1786.406 rows=464 loops=1)
> > Recheck Cond: (to_tsvector('english'::regconfig, message) @@ to_tsquery('131.211.112.9'::text))
>
> Well, there's your problem: the planner is off by a factor of about 500
> on its estimate of the number of rows matching this query, and that's
> what's causing it to pick the wrong plan. What you need to look into
> is getting that estimate to be more in sync with reality. Probably
> increasing the stats target for the message column would help.

But how can I get sane estimates for syslog data? Some searchstrings will
result in only a few hits, others in thousands of records or more.

Regards,

--
Henk van Lingen, ICT-SC Netwerk & Telefonie, (o- -+
Universiteit Utrecht, Jenalaan 18a, room 0.12 /\ |
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