From: Mark Mielke <mark@mark.mielke.cc>
To: Shoaib Mir <shoaibmir@gmail.com>
Cc: A. Kretschmer <andreas.kretschmer@schollglas.com>
Cc: pgsql-performance@postgresql.org
Subject: Re: count * performance issue
Date: Thu, 06 Mar 2008 01:26:46 -0500
Message-ID: <47CF8EA6.8070503@mark.mielke.cc> (raw)
In-Reply-To: <bf54be870803052215y5bb56235k5ea05ada1d701022@mail.gmail.com>
References: <f966c2ee0803052142l6a105678jfe2da92a0d9371@mail.gmail.com>
<f966c2ee0803052143k4570d771o6c300647d3b987d@mail.gmail.com>
<20080306060829.GA21084@a-kretschmer.de>
<bf54be870803052215y5bb56235k5ea05ada1d701022@mail.gmail.com>
>
> 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.
>
Of course, this means accepting the cost of obtaining update locks on
the count table.
The original poster should understand that they can either get a fast
estimated count, or they can get a slow accurate count (either slow in
terms of select using count(*) or slow in terms of updates using
triggers and locking).
Other systems have their own issues. An index scan may be faster than a
table scan for databases that can accurately determine counts using only
the index, but it's still a relatively slow operation, and people don't
normally need an accurate count for records in the range of 100,000+? :-)
Cheers,
mark
--
Mark Mielke <mark@mielke.cc>
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To: pgsql-performance@postgresql.org
Cc: mark@mark.mielke.cc, shoaibmir@gmail.com, andreas.kretschmer@schollglas.com
Subject: Re: count * performance issue
In-Reply-To: <47CF8EA6.8070503@mark.mielke.cc>
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