From: Tom Lane <tgl@sss.pgh.pa.us>
To: Michael Stone <mstone+postgres@mathom.us>
Cc: pgsql-performance@postgresql.org
Subject: Re: TB-sized databases
Date: Thu, 06 Dec 2007 11:13:18 -0500
Message-ID: <15753.1196957598@sss.pgh.pa.us> (raw)
In-Reply-To: <20071206154212.GP5294@mathom.us>
References: <4544e0330711260904g45d893a8ub1731e245aa8fc84@mail.gmail.com>
<13851.1196351131@sss.pgh.pa.us>
<1196352866.4246.1304.camel@ebony.site>
<200712051507.22745.xzilla@users.sourceforge.net>
<1196933896.4255.340.camel@ebony.site>
<20071206154212.GP5294@mathom.us>
Michael Stone <mstone+postgres@mathom.us> writes:
> OTOH, the planner can really screw up queries on really large databases.
> IIRC, the planner can use things like unique constraints to get some
> idea, e.g., of how many rows will result from a join. Unfortunately,
> the planner can't apply those techniques to certain constructs common in
> really large db's (e.g., partitioned tables--how do you do a unique
> constraint on a partitioned table?) I've got some queries that the
> planner thinks will return on the order of 10^30 rows for that sort of
> reason. In practice, the query may return 10^3 rows, and the difference
> between the seq scan and the index scan is the difference between a
> query that takes a few seconds and a query that I will never run to
> completion. I know the goal would be to make the planner understand
> those queries better,
Indeed, and if you've got examples where it's that far off, you should
report them.
regards, tom lane
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To: pgsql-performance@postgresql.org
Cc: tgl@sss.pgh.pa.us, mstone+postgres@mathom.us
Subject: Re: TB-sized databases
In-Reply-To: <15753.1196957598@sss.pgh.pa.us>
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