From: Tom Lane <tgl@sss.pgh.pa.us>
To: Steve Wampler <swampler@noao.edu>
Cc: Bruno Wolff III <bruno@wolff.to>
Cc: pgsql-sql@postgresql.org
Subject: Re: Make COUNT(*) Faster?
Date: Fri, 08 Jul 2005 11:35:00 -0400
Message-ID: <22916.1120836900@sss.pgh.pa.us> (raw)
In-Reply-To: <42CE96AF.3020903@noao.edu>
References: <9EF2931D-1097-470D-8ECB-59D00166C96F@apple.com>
<60vf3mklue.fsf@dba2.int.libertyrms.com>
<42CE89CA.2070607@noao.edu>
<20050708143508.GD22725@wolff.to>
<42CE96AF.3020903@noao.edu>
Steve Wampler <swampler@noao.edu> writes:
> So, leave COUNT(*) alone. But it would be very handy to have a
> way to get an approximate table size that is more accurate than is
> provided by a pg_class.reltuples that is only updated on vacuums.
If you want something cheap, you could use the same technique the
planner uses nowadays: take RelationGetNumberOfBlocks() (which is
guaranteed accurate) and multiply by reltuples/relpages. I don't
see anyplace where RelationGetNumberOfBlocks is directly exposed to
users now, but it'd be trivial to code up a couple of C functions to
provide this functionality.
regards, tom lane
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To: pgsql-sql@postgresql.org
Cc: tgl@sss.pgh.pa.us, swampler@noao.edu, bruno@wolff.to
Subject: Re: Make COUNT(*) Faster?
In-Reply-To: <22916.1120836900@sss.pgh.pa.us>
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