From: Bruce Momjian <bruce@momjian.us>
Message-Id: <201008221651.o7MGplA28857@momjian.us>
Subject: Re: Return of the Solaris vacuum polling problem --
	anyone remember this?
In-Reply-To: <15870.1282490621@sss.pgh.pa.us>
To: Tom Lane <tgl@sss.pgh.pa.us>
Date: Sun, 22 Aug 2010 12:51:47 -0400 (EDT)
CC: Josh Berkus <josh@agliodbs.com>,
	PostgreSQL-development <pgsql-hackers@postgresql.org>
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Tom Lane wrote:
> Bruce Momjian <bruce@momjian.us> writes:
> > We often mention that we do vacuum freeze for anti-wraparound vacuum,
> > but not for pg_clog file removal, which is the primary trigger for
> > autovacuum vacuum freezing.  I have added the attached documentation
> > patch for autovacuum_freeze_max_age;  back-patched to 9.0.
> 
> This patch does not actually seem like an improvement.  The paragraph is
> all about transaction age, but you've inserted something entirely
> unrelated, and not only that but chosen to make the unrelated thing seem
> like the major consequence and anti-wraparound an afterthought.

Well, the reason that value is 200 million is for pg_clog cleanup, not
for xid wraparound protection.  The next sentence does relate to xid
wraparound, but it seems to fit because the previous sentence ends with
xid wraparound:

	Note that the system will launch autovacuum processes to
	prevent wraparound even when autovacuum is otherwise disabled.

If we were worried about just xid wraparound I assume the value would be
2 billion.

Do you have a suggestion?  Reorder the items?

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

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