Date: Mon, 14 May 2007 18:16:19 -0400
From: Alvaro Herrera <alvherre@commandprompt.com>
To: Chris Browne <cbbrowne@acm.org>
Cc: pgsql-patches@postgresql.org
Subject: Re: [DOCS] Autovacuum and XID wraparound
Message-ID: <20070514221619.GC8916@alvh.no-ip.org>
References: <20070514011740.GH14860@fetter.org>
	<23394.1179108400@sss.pgh.pa.us> <1179117269.6047.3.camel@goldbach>
	<60sl9z6tln.fsf@dba2.int.libertyrms.com>
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Chris Browne wrote:

> Would the following 'maintenance' regimen be truly safe against XID
> wraparound:
> 
>  - Most tables are being vacuumed regularly, so that
>    pg_class.relfrozenxid is kept "safe."
> 
>  - There are some tables that periodically get TRUNCATEd so that, in
>    principle, they never need to be vacuumed.
> 
> Is it actually true that we'd never need to vacuum those tables
> (assuming 8.2+)?  I suppose it would be rather cheap to VACUUM
> immediately after the TRUNCATE...

You'd need to vacuum after the truncate.  It would be pretty cheap, the
tables being empty.

I suppose it would be pretty trivial to set the relfrozenxid to
RecentXmin or something during TRUNCATE.

-- 
Alvaro Herrera                                http://www.CommandPrompt.com/
The PostgreSQL Company - Command Prompt, Inc.