From: Simon Riggs <simon@2ndquadrant.com>
To: Tom Lane <tgl@sss.pgh.pa.us>
Cc: Alvaro Herrera <alvherre@alvh.no-ip.org>
Cc: Kevin Grittner <Kevin.Grittner@wicourts.gov>
Cc: pgsql-performance@postgresql.org
Subject: Re: Heavy write activity on first vacuum of fresh TOAST data
Date: Thu, 13 Dec 2007 19:20:43 +0000
Message-ID: <1197573643.4255.1877.camel@ebony.site> (raw)
In-Reply-To: <17873.1197571942@sss.pgh.pa.us>
References: <4760FF69.EE98.0025.0@wicourts.gov>
<1197562283.4255.1829.camel@ebony.site>
<476108F2.EE98.0025.0@wicourts.gov>
<476108F2.EE98.0025.0@wicourts.gov>
<13267.1197563721@sss.pgh.pa.us>
<47610BF3.EE98.0025.0@wicourts.gov>
<1197565242.4255.1853.camel@ebony.site>
<20071213172656.GL6262@alvh.no-ip.org>
<17873.1197571942@sss.pgh.pa.us>
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
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To: pgsql-performance@postgresql.org
Cc: simon@2ndquadrant.com, tgl@sss.pgh.pa.us, alvherre@alvh.no-ip.org, Kevin.Grittner@wicourts.gov
Subject: Re: Heavy write activity on first vacuum of fresh TOAST data
In-Reply-To: <1197573643.4255.1877.camel@ebony.site>
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