Re: HOT patch - version 15

From: Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>
To: "Pavan Deolasee" <pavan(dot)deolasee(at)gmail(dot)com>
Cc: "Bruce Momjian" <bruce(at)momjian(dot)us>, "Heikki Linnakangas" <heikki(at)enterprisedb(dot)com>, "Florian Pflug" <fgp(dot)phlo(dot)org(at)gmail(dot)com>, "Simon Riggs" <simon(at)2ndquadrant(dot)com>, "Gregory Stark" <stark(at)enterprisedb(dot)com>, PostgreSQL-patches <pgsql-patches(at)postgresql(dot)org>
Subject: Re: HOT patch - version 15
Date: 2007-09-11 02:11:04
Message-ID: 9103.1189476664@sss.pgh.pa.us
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"Pavan Deolasee" <pavan(dot)deolasee(at)gmail(dot)com> writes:
> Pruning removes intermediate dead tuples by marking their line pointers
> ~LP_USED and redirecting the root line pointer to the first
> live/recently_dead tuple in the chain.

It seems utterly unsafe to do this without a vacuum-grade lock on the
page. Someone might be examining the root tuple (eg, in a SnapshotAny
scan) and I think they are entitled to assume that the line pointer
stays valid while they are looking at the tuple.

regards, tom lane

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