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Re: Dead Space Map

From: "Jim C(dot) Nasby" <jnasby(at)pervasive(dot)com>
To: Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>
Cc: Heikki Linnakangas <hlinnaka(at)iki(dot)fi>, pgsql-hackers(at)postgresql(dot)org
Subject: Re: Dead Space Map
Date: 2006-02-27 23:39:06
Message-ID: (view raw or whole thread)
Lists: pgsql-hackers
On Mon, Feb 27, 2006 at 01:17:36PM -0500, Tom Lane wrote:
> > * vacuuming pages one by one as they're written by bgwriter
> That's not happening.  VACUUM has to be a transaction and the bgwriter
> does not run transactions; nor is it in any position to clean out index
> entries associated with a heap page.  (To change this would at a minimum
> require instituting a separate bgwriter process per database; or else a
> wholesale rewrite of our catalog access infrastructure to allow it to
> work in a non-database-specific context.  There are also interesting
> deadlock problems to think about if the bgwriter can be blocked by other
> transactions, or if it needs to read pages not currently in shared memory.)

Or there could be a seperate daemon that isn't associated with bgwriter.
AFAIK as long as it vacuums the dirty page before bgwrite wants to write
it you'd still get the IO benefit.
Jim C. Nasby, Sr. Engineering Consultant      jnasby(at)pervasive(dot)com
Pervasive Software    work: 512-231-6117
vcard:       cell: 512-569-9461

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