From: A. Kretschmer <andreas.kretschmer@schollglas.com>
To: pgsql-performance@postgresql.org
Subject: Re: count * performance issue
Date: Thu, 6 Mar 2008 07:08:29 +0100
Message-ID: <20080306060829.GA21084@a-kretschmer.de> (raw)
In-Reply-To: <f966c2ee0803052143k4570d771o6c300647d3b987d@mail.gmail.com>
References: <f966c2ee0803052142l6a105678jfe2da92a0d9371@mail.gmail.com>
<f966c2ee0803052143k4570d771o6c300647d3b987d@mail.gmail.com>
am Thu, dem 06.03.2008, um 11:13:01 +0530 mailte sathiya psql folgendes:
> count(*) tooks much time...
>
> but with the where clause we can make this to use indexing,... what where
> clause we can use??
An index without a WHERE can't help to avoid a seq. scan.
>
> Am using postgres 7.4 in Debian OS with 1 GB RAM,
PG 7.4 are very old... Recent versions are MUCH faster.
>
> am having a table with nearly 50 lakh records,
>
> it has more than 15 columns, i want to count how many records are there, it is
> taking nearly 17 seconds to do that...
>
> i know that to get a approximate count we can use
> SELECT reltuples FROM pg_class where relname = TABLENAME;
>
> but this give approximate count, and i require exact count...
There aren't a general solution. If you realy need the exact count of
tuples than you can play with a TRIGGER and increase/decrease the
tuple-count for this table in an extra table.
Andreas
--
Andreas Kretschmer
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To: pgsql-performance@postgresql.org
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Subject: Re: count * performance issue
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