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Cc: Tom Lane <tgl@sss.pgh.pa.us>, Josh Berkus <josh@agliodbs.com>,
	PostgreSQL-development <pgsql-hackers@postgresql.org>
Subject: Re: Return of the Solaris vacuum polling problem -- anyone remember
	this?
From: Alvaro Herrera <alvherre@commandprompt.com>
To: Bruce Momjian <bruce@momjian.us>
In-reply-to: <201008231855.o7NItt310271@momjian.us>
References: <201008231855.o7NItt310271@momjian.us>
Date: Mon, 23 Aug 2010 15:19:54 -0400
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Excerpts from Bruce Momjian's message of lun ago 23 14:55:55 -0400 2010:

> 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?

I think the new para doesn't make much sense, in context.  Why does it
say "freeze"?  How can we expect users to understand how that is
related to this parameter?

> --- 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.

-- 
Álvaro Herrera <alvherre@commandprompt.com>
The PostgreSQL Company - Command Prompt, Inc.
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