Date: Thu, 22 Mar 2007 10:18:10 -0400
From: Michael Stone <mstone+postgres@mathom.us>
Subject: Re: Performance of count(*)
In-reply-to: <Pine.LNX.4.64.0703221323590.1503@ismoli.solenovo.jns>
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References: <Pine.LNX.4.62.0703221149210.13747@wr-linux02>
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On Thu, Mar 22, 2007 at 01:30:35PM +0200, ismo.tuononen@solenovo.fi wrote:
>approximated count?????
>
>why? who would need it? where you can use it?

Do a google query. Look at the top of the page, where it says 
"results N to M of about O". For user interfaces (which is where a lot 
of this count(*) stuff comes from) you quite likely don't care about the 
exact count, because the user doesn't really care about the exact count. 

IIRC, that's basically what you get with the mysql count anyway, since 
there are corner cases for results in a transaction. Avoiding those 
cases is why the postgres count takes so long; sometimes that's what's 
desired and sometimes it is not.

Mike Stone