From: Josh Berkus <josh@agliodbs.com>
To: pgsql-performance@postgresql.org
Subject: Re: vacuum internals and performance affect
Date: Thu, 01 Dec 2011 10:01:57 -0800
Message-ID: <4ED7C115.4010607@agliodbs.com> (raw)
In-Reply-To: <1322688860656-5036800.post@n5.nabble.com>
References: <1322586733308-5033043.post@n5.nabble.com>
<4ED69DCD.5000806@agliodbs.com>
<1322688860656-5036800.post@n5.nabble.com>
MirrorX,
> so when a transaction is still open from a while back (according to the
> transactionID), no 'new dead' tuples can be marked as re-usable space for
> new rows, right? by 'new dead' i mean that for example there is a
> transaction running from 10.00am(with a specific transactionID). when i
> delete rows at 11.00am these are the ones i am referring to.
With the understanding that what we're actually checking is snapshots
(which are not completely linear) and not timestamps, yes, that's a good
simplification for what happens.
> but, for these rows, the 'deleted' ones. does vacuum do anything at all at
> that time? and if so, what is it? thx in advance
No, it does nothing. What would it do?
--
Josh Berkus
PostgreSQL Experts Inc.
http://pgexperts.com
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To: pgsql-performance@postgresql.org
Cc: josh@agliodbs.com
Subject: Re: vacuum internals and performance affect
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