From: Tom Lane <tgl@sss.pgh.pa.us>
To: Jordi <jmaillists@promani.be>
cc: pgsql-performance@postgresql.org
Subject: Re: Bitmap and-ing between btree and gin?
In-reply-to: <56B332B6.1040109@promani.be>
References: <56B332B6.1040109@promani.be>
Comments: In-reply-to Jordi <jmaillists@promani.be>
 message dated "Thu, 04 Feb 2016 12:15:02 +0100"
Date: Thu, 04 Feb 2016 11:08:41 -0500
Message-ID: <17855.1454602121@sss.pgh.pa.us>
Precedence: bulk
Sender: pgsql-performance-owner@postgresql.org

Jordi <jmaillists@promani.be> writes:
> I've been trying to get a query use indexes and it has raised a doubt 
> whether pgsql supports bitmap and-ing between a multi-column btree index 
> and a gin index.

Sure.  But such a plan would give an unordered result, meaning that we'd
have to process the whole table before doing the ORDER BY/LIMIT.  The
planner evidently thinks that it's better to try to process the rows in
ID order so it can stop as soon as it's got 100.  If it's wrong about
that, that's likely because it's got a bad estimate of the selectivity of
the other WHERE conditions.  You might see if you can improve the
statistics for the search_vector column.

			regards, tom lane


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