Message-ID: <4F4B9AB9.6000900@peak6.com>
Date: Mon, 27 Feb 2012 09:01:13 -0600
From: Shaun Thomas <sthomas@peak6.com>
Reply-To: <sthomas@peak6.com>
Organization: Peak6
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To: Andrew Dunstan <andrew@dunslane.net>
CC: "Reuven M. Lerner" <reuven@lerner.co.il>,
	<pgsql-performance@postgresql.org>
Subject: Re: Very long deletion time on a 200 GB database
References: <4F45FB55.1020600@lerner.co.il>
	<4F47C6C4.6030102@pinpointresearch.com>
	<4F4B39EF.2080004@lerner.co.il> <4F4B9721.6050808@peak6.com>
	<4F4B9907.60008@dunslane.net>
In-Reply-To: <4F4B9907.60008@dunslane.net>
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On 02/27/2012 08:53 AM, Andrew Dunstan wrote:

> If he has autovacuum on he could well be just fine with his proposed
> strategy. Or he could have tables partitioned by time and do the delete
> by just dropping partitions. There are numerous way he could get this to
> work.

He isn't using partitions though. That's the whole reason for this 
thread. Having autovacuum turned on (which should be the case for 8.4 
and above anyway) will not magically remove the old rows. VACUUM marks 
rows as dead/reusable, so INSERT and UPDATE statements will take the 
dead spots instead of creating new extents.

Like I said, this will stop his tables from growing further so long as 
he keeps his maintenance functions running regularly from now on, but 
the existing rows he's trying to delete will never go away until he runs 
a CLUSTER or some other system of actually purging the dead rows.

Notice how I don't suggest using VACUUM FULL. :)

-- 
Shaun Thomas
OptionsHouse | 141 W. Jackson Blvd. | Suite 500 | Chicago IL, 60604
312-444-8534
sthomas@peak6.com

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