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From: Bruce Momjian <bruce@momjian.us>
Message-Id: <201008231855.o7NItt310271@momjian.us>
Subject: Re: Return of the Solaris vacuum polling problem --
	anyone remember this?
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To: Alvaro Herrera <alvherre@commandprompt.com>
Date: Mon, 23 Aug 2010 14:55:55 -0400 (EDT)
CC: Tom Lane <tgl@sss.pgh.pa.us>, Josh Berkus <josh@agliodbs.com>,
	PostgreSQL-development <pgsql-hackers@postgresql.org>
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Alvaro Herrera wrote:
> Excerpts from Tom Lane's message of lun ago 23 12:40:32 -0400 2010:
> > Alvaro Herrera <alvherre@commandprompt.com> writes:
> > > Excerpts from Bruce Momjian's message of dom ago 22 12:51:47 -0400 2010:
> > >> Do you have a suggestion?  Reorder the items?
> > 
> > > I'd add another para before that one saying that this value "also"
> > > affects pg_clog truncation.  I agree that putting pg_clog truncation as
> > > the first item here is not an improvement.  For most people, having
> > > those pg_clog files there or not is going to be a wash, compared to data
> > > size.
> > 
> > I was going to suggest that the point about pg_clog should be in a
> > separate paragraph *after* this one, since it seems like a secondary
> > issue.  But anyway, I agree with putting this para back as it was and
> > talking about clog in a separate para.
> 
> Sorry, yes, I was also thinking "after".  I don't know what made me
> write "before" but it wasn't clarity of thought.

OK, I have attached a proposed patch to improve this.  I moved the
pg_clog mention to a new paragraph and linked it to the reason the
default is relatively low.

Comments?

-- 
  Bruce Momjian  <bruce@momjian.us>        http://momjian.us
  EnterpriseDB                             http://enterprisedb.com

  + It's impossible for everything to be true. +

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Index: doc/src/sgml/config.sgml
===================================================================
RCS file: /cvsroot/pgsql/doc/src/sgml/config.sgml,v
retrieving revision 1.307
diff -c -c -r1.307 config.sgml
*** doc/src/sgml/config.sgml	23 Aug 2010 02:43:25 -0000	1.307
--- doc/src/sgml/config.sgml	23 Aug 2010 18:55:02 -0000
***************
*** 4150,4161 ****
         <para>
          Specifies the maximum age (in transactions) that a table's
          <structname>pg_class</>.<structfield>relfrozenxid</> field can
!         attain before a <command>VACUUM</> operation is forced to allow removal
!         of old files from the <filename>pg_clog</> subdirectory and prevent
!         transaction ID wraparound within the table.  Note that the system
!         will launch autovacuum processes to prevent wraparound even when
!         autovacuum is otherwise disabled.
!         The default is 200 million transactions.
          This parameter can only be set at server start, but the setting
          can be reduced for individual tables by
          changing storage parameters.
--- 4150,4165 ----
         <para>
          Specifies the maximum age (in transactions) that a table's
          <structname>pg_class</>.<structfield>relfrozenxid</> field can
!         attain before a <command>VACUUM</> freeze operation is forced
!         to prevent transaction ID wraparound within the table.
!         Note that the system will launch autovacuum processes to
!         prevent wraparound even when autovacuum is otherwise disabled.
!        </para>
! 
!        <para>
!         Vacuum freeze also allows removal of old files from the
!         <filename>pg_clog</> subdirectory, which is why the default
!         is a relatively low 200 million transactions.
          This parameter can only be set at server start, but the setting
          can be reduced for individual tables by
          changing storage parameters.

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