From: Heikki Linnakangas <heikki.linnakangas@enterprisedb.com>
To: Gregory Stark <stark@enterprisedb.com>
Cc: Bruce Momjian <bruce@momjian.us>
Cc: PostgreSQL-development <pgsql-hackers@postgresql.org>
Cc: Tom Lane <tgl@sss.pgh.pa.us>
Subject: Re: Visibility map, partial vacuums
Date: Thu, 15 Jan 2009 08:30:34 +0200
Message-ID: <496ED80A.2080804@enterprisedb.com> (raw)
In-Reply-To: <87wscxfisu.fsf@oxford.xeocode.com>
References: <200901150055.n0F0tLK27057@momjian.us>
<87wscxfisu.fsf@oxford.xeocode.com>
Gregory Stark wrote:
> Bruce Momjian <bruce@momjian.us> writes:
>
>> Would someone tell me why 'autovacuum_freeze_max_age' defaults to 200M
>> when our wraparound limit is around 2B?
>
> I suggested raising it dramatically in the post you quote and Heikki pointed
> it controls the maximum amount of space the clog will take. Raising it to,
> say, 800M will mean up to 200MB of space which might be kind of annoying for a
> small database.
>
> It would be nice if we could ensure the clog got trimmed frequently enough on
> small databases that we could raise the max_age. It's really annoying to see
> all these vacuums running 10x more often than necessary.
Well, if it's a small database, you might as well just vacuum it.
> The rest of the thread is visible at the bottom of:
>
> http://article.gmane.org/gmane.comp.db.postgresql.devel.general/107525
>
>> Also, is anything being done about the concern about 'vacuum storm'
>> explained below?
>
> I'm interested too.
The additional "vacuum_freeze_table_age" (as I'm now calling it) setting
I discussed in a later thread should alleviate that somewhat. When a
table is autovacuumed, the whole table is scanned to freeze tuples if
it's older than vacuum_freeze_table_age, and relfrozenxid is advanced.
When different tables reach the autovacuum threshold at different times,
they will also have their relfrozenxids set to different values. And in
fact no anti-wraparound vacuum is needed.
That doesn't help with read-only or insert-only tables, but that's not a
new problem.
--
Heikki Linnakangas
EnterpriseDB http://www.enterprisedb.com
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To: pgsql-hackers@postgresql.org
Cc: heikki.linnakangas@enterprisedb.com, stark@enterprisedb.com, bruce@momjian.us, tgl@sss.pgh.pa.us
Subject: Re: Visibility map, partial vacuums
In-Reply-To: <496ED80A.2080804@enterprisedb.com>
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