From: | Alan Hodgson <ahodgson(at)simkin(dot)ca> |
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To: | pgsql-general(at)postgresql(dot)org |
Subject: | Re: more problems with count(*) on large table |
Date: | 2007-10-01 17:12:05 |
Message-ID: | 200710011012.05779@hal.medialogik.com |
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Lists: | pgsql-general |
On Monday 01 October 2007, Mike Charnoky <noky(at)nextbus(dot)com> wrote:
> This is strange... count(*) operations over a period of one day's worth
> of data now take ~1-2 minutes to run or ~40 minutes. It seems that the
> first time the data is queried it takes about 40 minutes. If I try the
> query again, it finishes in 1-2 minutes!
>
> Again, nothing else is happening on this db server except for a constant
> insertion into this table and a few others. I have done "set statistics
> 100" for the evtime field in this table.
The first time, you're reading from disk. The second time, you're reading
from cache. Tens of millions of disk seeks don't come cheap.
--
We're Microsoft. Everything else is just patent infringement.
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