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: | 20060227233906.GT82012@pervasive.com |
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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 http://pervasive.com work: 512-231-6117
vcard: http://jim.nasby.net/pervasive.vcf cell: 512-569-9461
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