From: | Martijn van Oosterhout <kleptog(at)svana(dot)org> |
---|---|
To: | Simon Riggs <simon(at)2ndquadrant(dot)com> |
Cc: | pgsql-hackers(at)postgresql(dot)org |
Subject: | Re: Improving count(*) |
Date: | 2005-11-17 19:38:16 |
Message-ID: | 20051117193816.GH22933@svana.org |
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Lists: | pgsql-hackers |
On Thu, Nov 17, 2005 at 07:28:10PM +0000, Simon Riggs wrote:
> One of the major complaints is always "Select count(*) is slow".
>
> I have a somewhat broadbrush idea as to how we might do this (for larger
> tables).
It's an interesting idea, but you still run into the issue of
visibility. If two people start a transaction, one of them inserts a
row and then both run a select count(*), they should get different
answers. I just don't see a way that your suggestion could possibly
lead to that result...
There is no unique answer to count(*), it all depends on who is looking
(sounds like relativity :) ). If you can sort that, you're well over
90% of the way.
Have a nice day,
--
Martijn van Oosterhout <kleptog(at)svana(dot)org> http://svana.org/kleptog/
> Patent. n. Genius is 5% inspiration and 95% perspiration. A patent is a
> tool for doing 5% of the work and then sitting around waiting for someone
> else to do the other 95% so you can sue them.
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