From: Simon Riggs <simon@2ndquadrant.com>
To: 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 18:12:44 +0000
Message-ID: <1197569564.4255.1855.camel@ebony.site> (raw)
In-Reply-To: <47611B9D.EE98.0025.0@wicourts.gov>
References: <4760FF69.EE98.0025.0@wicourts.gov>
<1197562283.4255.1829.camel@ebony.site>
<47611B9D.EE98.0025.0@wicourts.gov>
On Thu, 2007-12-13 at 11:46 -0600, Kevin Grittner wrote:
> >>> On Thu, Dec 13, 2007 at 10:11 AM, in message
> <camel@ebony.site/">1197562283.4255.1829.camel@ebony.site>, Simon Riggs <simon@2ndquadrant.com>
> wrote:
> > On Thu, 2007-12-13 at 09:46 -0600, Kevin Grittner wrote:
> >
> >> The data was inserted through a Java program using a prepared
> >> statement with no indexes on the table. The primary key was then
> >> added, and now I've started a vacuum. The new table wound up being
> >> the first big table vacuumed, and I noticed something odd. Even
> >> though there have been no rollbacks, updates, or deletes on this
> >> table, the vacuum is writing as much as it is reading while dealing
> >> with the TOAST data.
> >
> > Writing hint bits. Annoying isn't it? :-(
>
> Is there anything in the documentation that mentions this pattern
> of activity? Since I started clearing the WAL file tails before
> compression, it has surprised me how much WAL file activity there
> is from the nightly vacuum. I had assumed that some part of this
> was freezing old tuples, but that didn't seem to exactly match the
> pattern of activity. If the hint bit changes are written to the
> WAL, I think this explains it.
They're not.
--
Simon Riggs
2ndQuadrant http://www.2ndQuadrant.com
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To: pgsql-performance@postgresql.org
Cc: simon@2ndquadrant.com, Kevin.Grittner@wicourts.gov
Subject: Re: Heavy write activity on first vacuum of fresh TOAST data
In-Reply-To: <1197569564.4255.1855.camel@ebony.site>
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