Skip site navigation (1) Skip section navigation (2)

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: 20060227233906.GT82012@pervasive.com (view raw or flat)
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      http://pervasive.com    work: 512-231-6117
vcard: http://jim.nasby.net/pervasive.vcf       cell: 512-569-9461

In response to

pgsql-hackers by date

Next:From: Jim C. NasbyDate: 2006-02-27 23:44:56
Subject: Re: Dead Space Map
Previous:From: Tom LaneDate: 2006-02-27 23:20:36
Subject: Re: Scrollable cursors and Sort performance

Privacy Policy | About PostgreSQL
Copyright © 1996-2014 The PostgreSQL Global Development Group