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Re: PG writes a lot to the disk

From: Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>
To: Bill Moran <wmoran(at)collaborativefusion(dot)com>
Cc: "Albe Laurenz" <laurenz(dot)albe(at)wien(dot)gv(dot)at>, "Laurent Raufaste *EXTERN*" <analogue(at)glop(dot)org>, pgsql-performance(at)postgresql(dot)org
Subject: Re: PG writes a lot to the disk
Date: 2008-03-20 15:20:39
Message-ID: 10279.1206026439@sss.pgh.pa.us (view raw or flat)
Thread:
Lists: pgsql-performance
Bill Moran <wmoran(at)collaborativefusion(dot)com> writes:
> However, the part I wanted to comment on (and got busy yesterday so
> am only getting to it now) is that there's no guarantee that SELECT
> isn't modifying rows.

Another way that SELECT can cause disk writes is if it sets hint bits on
recently-committed rows.  However, if the tables aren't actively being
modified any more, you'd expect that sort of activity to settle out pretty
quickly.

I concur with the temporary-file theory --- it's real hard to see how
analyzing the tables would've fixed it otherwise.

			regards, tom lane

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