From: Tom Lane <tgl@sss.pgh.pa.us>
To: Jeff Davis <pgsql@j-davis.com>
Cc: pgsql-performance@postgresql.org
Subject: Re: explanation for seeks in VACUUM
Date: Fri, 14 Dec 2007 19:04:50 -0500
Message-ID: <15476.1197677090@sss.pgh.pa.us> (raw)
In-Reply-To: <1197660594.28804.276.camel@dogma.ljc.laika.com>
References: <1197660594.28804.276.camel@dogma.ljc.laika.com>
Jeff Davis <pgsql@j-davis.com> writes:
> Where am I going wrong? Are many of these lseeks no-ops or something?
They're not supposed to be, but if you only tracked seeks and not
reads or writes, it's hard to be sure what's going on.
8.2's VACUUM should process a btree index (this is a btree index no?)
in physical order, so I'd expect lseeks only when a page is already in
buffers --- at least on the read side. On the write side things might
be a great deal less predictable. You're cleaning out about one tuple
in 30, so the odds are that nearly every index page is getting dirtied,
and they're going to need to be written sometime.
regards, tom lane
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To: pgsql-performance@postgresql.org
Cc: tgl@sss.pgh.pa.us, pgsql@j-davis.com
Subject: Re: explanation for seeks in VACUUM
In-Reply-To: <15476.1197677090@sss.pgh.pa.us>
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