Re: pg_trgm indexes giving bad estimations?

From: Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>
To: Ben <bench(at)silentmedia(dot)com>
Cc: pgsql-performance(at)postgresql(dot)org
Subject: Re: pg_trgm indexes giving bad estimations?
Date: 2006-10-05 01:54:27
Message-ID: 5872.1160013267@sss.pgh.pa.us
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Ben <bench(at)silentmedia(dot)com> writes:
> How can I get the planner to not expect so many rows to be returned?

Write an estimation function for the pg_trgm operator(s). (Send in a
patch if you do!) I see that % is using "contsel" which is only a stub,
and would likely be wrong for % even if it weren't.

> A possibly related question is: because pg_tgrm lets me set the
> matching threshold of the % operator, how does that affect the planner?

It hasn't a clue about that.

regards, tom lane

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