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Re: I/O on select count(*)
- From: PFC <lists(at)peufeu(dot)com>
- To: "Greg Smith" <gsmith(at)gregsmith(dot)com>, "Matthew Wakeling" <matthew(at)flymine(dot)org>
- Cc: pgsql-performance(at)postgresql(dot)org
- Subject: Re: I/O on select count(*)
- Date: Mon, 19 May 2008 19:14:48 +0200
- Message-id: <op(dot)ubeviyrgcigqcu(at)apollo13(dot)peufeu(dot)com>
The real question in my mind is why this turns into a bottleneck before the similar task of cleaning the 16MB XLOG segment does. I expected that one would need to be cracked before the CLOG switch time could possibly be an issue, but reports from the field seem to suggest otherwise.
Hm, on current CPUs zeroing 8kB of RAM should take less than 2 us... now if it has to be written to disk, that's another story !
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