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Re: Problem with pg_upgrade?

From: Bruce Momjian <bruce(at)momjian(dot)us>
To: Alvaro Herrera <alvherre(at)commandprompt(dot)com>
Cc: Jeff Davis <pgsql(at)j-davis(dot)com>, PostgreSQL-development <pgsql-hackers(at)postgresql(dot)org>
Subject: Re: Problem with pg_upgrade?
Date: 2011-03-30 14:57:32
Message-ID: (view raw, whole thread or download thread mbox)
Lists: pgsql-hackers
Alvaro Herrera wrote:
> Excerpts from Jeff Davis's message of mar mar 29 21:27:34 -0300 2011:
> > On Tue, 2011-03-29 at 15:52 -0400, Bruce Momjian wrote:
> > > Does anyone have any other suggestions on how to make sure autovacuum
> > > does not run in freeze mode?
> > 
> > Can you run in single user mode?
> I asked the same thing.  Apparently the problem is that it would make
> error handling a lot more difficult.  I think it would be better to have
> some sort of option to disable autovacuum completely which would be used
> only during pg_upgrade.

Yes, also consider that pg_dumpall assumes psql with its use of
\connect, and I would have to start/stop the single-user backend for
every database change, plus I use psql with ON_ERROR_STOP=on.

I think we have three options:

	o  find if the use of autovacuum_freeze_max_age is safe, or make
	   it safe
	o  document that autovacuum_naptime always happens before
	   autovacuum does anything and set it high
	o  modify autovacuum to be an enum, with values on/off/disabled

I think the last one makes more sense, and is safer if we need to
backpatch this.  Creating a new variable for this would be confusing
because it could conflict with the 'autovacuum' setting.

Also, I am unclear if this is really our bug.  At least one of the
systems was on Ubuntu/Debian, and they might both have been, and I know
Debian changes our source code.  Where can I find a copy of the diffs
they have made?

I am hearing only second-hand reports of this problem through
Rhodiumtoad on IRC.  I don't have IRC access this week so if someone can
get details from him that would help.  I think the fix he found was to
pull the clog files off of an old file system backup.

  Bruce Momjian  <bruce(at)momjian(dot)us>

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

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