Re: Dead Space Map for vacuum

From: Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>
To: "Simon Riggs" <simon(at)2ndquadrant(dot)com>
Cc: "Heikki Linnakangas" <heikki(at)enterprisedb(dot)com>, "Gavin Sherry" <swm(at)linuxworld(dot)com(dot)au>, "ITAGAKI Takahiro" <itagaki(dot)takahiro(at)oss(dot)ntt(dot)co(dot)jp>, pgsql-hackers(at)postgresql(dot)org
Subject: Re: Dead Space Map for vacuum
Date: 2006-12-29 15:49:55
Message-ID: 2589.1167407395@sss.pgh.pa.us
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"Simon Riggs" <simon(at)2ndquadrant(dot)com> writes:
> I would suggest that we tracked whether a block has had 0, 1 or 1+
> updates/deletes against it. When a block has 1+ it can then be
> worthwhile to VACUUM it and to place it onto the FSM. Two dead tuples is
> really the minimum space worth reclaiming on any block.

How do you arrive at that conclusion?

Counterexample: table in which all tuples exceed half a page.

regards, tom lane

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