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Re: Dead Space Map

From: Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>
To: Greg Stark <gsstark(at)mit(dot)edu>
Cc: Bruce Momjian <pgman(at)candle(dot)pha(dot)pa(dot)us>, "Jim C(dot) Nasby" <jnasby(at)pervasive(dot)com>, Heikki Linnakangas <hlinnaka(at)iki(dot)fi>, pgsql-hackers(at)postgresql(dot)org
Subject: Re: Dead Space Map
Date: 2006-02-28 18:08:17
Message-ID: 16849.1141150097@sss.pgh.pa.us (view raw or flat)
Thread:
Lists: pgsql-hackers
Greg Stark <gsstark(at)mit(dot)edu> writes:
> I originally thought you meant if you are repeatedly updating the same record
> within the same transaction. In that case sure you could reuse the space but
> a) only if it's big enough for the new record and b) how often do you really
> do that?

Also, it's not that easy even within a single transaction: you could
have active snapshots inside your xact that can still see the obsoleted
tuple.

			regards, tom lane

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