Alvaro Herrera wrote:
> Excerpts from Tom Lane's message of lun ago 23 12:40:32 -0400 2010:
> > Alvaro Herrera <alvhe...@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 <br...@momjian.us> http://momjian.us
EnterpriseDB http://enterprisedb.com
+ It's impossible for everything to be true. +
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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