Subject: Re: Heavy write activity on first vacuum of fresh TOAST
	data
From: Simon Riggs <simon@2ndquadrant.com>
To: Tom Lane <tgl@sss.pgh.pa.us>
Cc: Alvaro Herrera <alvherre@alvh.no-ip.org>,
	Kevin Grittner <Kevin.Grittner@wicourts.gov>,
	pgsql-performance@postgresql.org
In-Reply-To: <17873.1197571942@sss.pgh.pa.us>
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Date: Thu, 13 Dec 2007 19:20:43 +0000
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On Thu, 2007-12-13 at 13:52 -0500, Tom Lane wrote:
> Alvaro Herrera <alvherre@alvh.no-ip.org> writes:
> > Simon Riggs wrote:
> >> We might be able to have bgwriter set hint bits on dirty blocks,
> 
> > I don't think that works, because the bgwriter has no access to the
> > catalogs, therefore it cannot examine the page contents.  To bgwriter,
> > pages are opaque.
> 
> Another issue is that this'd require bgwriter to access the clog SLRU
> area.  I seem to remember worrying that that could lead to low-level
> deadlocks, though I cannot recall the exact case at the moment.
> Even without that, it would increase contention for SLRU, which we
> probably don't want.

I was trying to highlight the problems, not advocate that as an
approach, sorry if I wasn't clear enough. Even if you solved the
problems both of you have mentioned I don't think the dynamic behaviour
will be useful enough to merit the effort of trying. I'm definitely not
going to be spending any time on this. Fish are frying elsewhere.

-- 
  Simon Riggs
  2ndQuadrant  http://www.2ndQuadrant.com