From: Florian G. Pflug <fgp@phlo.org>
To: Tom Lane <tgl@sss.pgh.pa.us>
Cc: ITAGAKI Takahiro <itagaki.takahiro@oss.ntt.co.jp>
Cc: pgsql-hackers@postgresql.org
Cc: pgsql-patches@postgresql.org
Subject: Re: Aggressive freezing in lazy-vacuum
Date: Mon, 05 Mar 2007 20:26:58 +0100
Message-ID: <45EC6F02.1050306@phlo.org> (raw)
In-Reply-To: <18982.1173110551@sss.pgh.pa.us>
References: <20070227141958.638D.ITAGAKI.TAKAHIRO@oss.ntt.co.jp>
<20070227170613.GK29041@nasby.net>
<20070305182401.C4BC.ITAGAKI.TAKAHIRO@oss.ntt.co.jp>
<18982.1173110551@sss.pgh.pa.us>
Tom Lane wrote:
> ITAGAKI Takahiro <itagaki.takahiro@oss.ntt.co.jp> writes:
>> This is a stand-alone patch for aggressive freezing. I'll propose
>> to use OldestXmin instead of FreezeLimit as the freeze threshold
>> in the circumstances below:
>
> I think it's a really bad idea to freeze that aggressively under any
> circumstances except being told to (ie, VACUUM FREEZE). When you
> freeze, you lose history information that might be needed later --- for
> forensic purposes if nothing else. You need to show a fairly amazing
> performance gain to justify that, and I don't think you can.
There could be a GUC vacuum_freeze_limit, and the actual FreezeLimit
would be calculated as
GetOldestXmin() - vacuum_freeze_limit
The default for vacuum_freeze_limit would be MaxTransactionId/2, just
as it is now.
greetings, Florian Pflug
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Reply to all the recipients using the --to and --cc options:
reply via email
To: pgsql-performance@postgresql.org
Cc: fgp@phlo.org, tgl@sss.pgh.pa.us, itagaki.takahiro@oss.ntt.co.jp, pgsql-hackers@postgresql.org, pgsql-patches@postgresql.org
Subject: Re: Aggressive freezing in lazy-vacuum
In-Reply-To: <45EC6F02.1050306@phlo.org>
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
This inbox is served by DDX for PostgreSQL; see mirroring instructions
for how to clone and mirror all data and code used for this inbox