From: Neil Whelchel <neil.whelchel@gmail.com>
To: pgsql-performance@postgresql.org <pgsql-performance@postgresql.org>
Subject: Re: Slow count(*) again...
Date: Mon, 11 Oct 2010 19:36:45 -0700
Message-ID: <201010111936.46207.neil.whelchel@gmail.com> (raw)
In-Reply-To: <4CB3A2CC.9070009@vmsinfo.com>
References: <201010091626.18636.neil.whelchel@gmail.com>
<201010111254.58479.neil.whelchel@gmail.com>
<4CB3A2CC.9070009@vmsinfo.com>
On Monday 11 October 2010 16:50:36 you wrote:
> On 10/11/2010 3:54 PM, Neil Whelchel wrote:
> > 1. A faster count(*), or something like my proposed estimate(*).
> > 2. A way to get the total rows matched when using LIMIT and OFFSET before
> > LIMIT and OFFSET are applied.
>
> The biggest single problem with "select count(*)" is that it is
> seriously overused. People use that idiom to establish existence, which
> usually leads to a performance disaster in the application using it,
> unless the table has no more than few hundred records. SQL language, of
> which PostgreSQL offers an excellent implementation, offers [NOT]
> EXISTS clause since its inception in the Jurassic era. The problem is
> with the sequential scan, not with counting. I'd even go as far as to
> suggest that 99% instances of the "select count(*)" idiom are probably
> bad use of the SQL language.
I agree, I have seen many very bad examples of using count(*). I will go so
far as to question the use of count(*) in my examples here. It there a better
way to come up with a page list than using count(*)? What is the best method
to make a page of results and a list of links to other pages of results? Am I
barking up the wrong tree here?
-Neil-
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Subject: Re: Slow count(*) again...
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