From: Tom Lane <tgl@sss.pgh.pa.us>
To: Denis de Bernardy <ddebernardy@yahoo.com>
Cc: pgsql-performance@postgresql.org <pgsql-performance@postgresql.org>
Subject: Re: row estimate very wrong for array type
Date: Wed, 04 May 2011 10:12:49 -0400
Message-ID: <10497.1304518369@sss.pgh.pa.us> (raw)
In-Reply-To: <625605.72736.qm@web112406.mail.gq1.yahoo.com>
References: <625605.72736.qm@web112406.mail.gq1.yahoo.com>
Denis de Bernardy <ddebernardy@yahoo.com> writes:
> [ estimates for array && suck ]
> Might this be a bug in the operator's selectivity, or am I doing something wrong?
Array && uses areasel() which is only a stub :-(
In the particular case here it'd be possible to get decent answers
just by trying the operator against all the MCV-list entries, but it's
unlikely that that would fix things for enough people to be worth the
trouble. Really you'd need to maintain statistics about the element
values appearing in the array column in order to get useful estimates
for && queries. Jan Urbanski did something similar for tsvector columns
a year or two ago, but nobody's gotten around to doing it for array
columns.
regards, tom lane
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To: pgsql-performance@postgresql.org
Cc: tgl@sss.pgh.pa.us, ddebernardy@yahoo.com
Subject: Re: row estimate very wrong for array type
In-Reply-To: <10497.1304518369@sss.pgh.pa.us>
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