Re: Latest plans for Utilities with HOT

From: "Simon Riggs" <simon(at)2ndquadrant(dot)com>
To: "Pavan Deolasee" <pavan(at)enterprisedb(dot)com>
Cc: "Pavan Deolasee" <pavan(dot)deolasee(at)enterprisedb(dot)com>, <pgsql-hackers(at)postgresql(dot)org>, "Heikki Linnakangas" <heikki(at)enterprisedb(dot)com>, "Nikhil S" <nikhil(dot)sontakke(at)enterprisedb(dot)com>
Subject: Re: Latest plans for Utilities with HOT
Date: 2007-03-06 12:02:19
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On Mon, 2007-03-05 at 22:25 +0530, Pavan Deolasee wrote:
> Simon Riggs wrote:
> > On Mon, 2007-03-05 at 21:39 +0530, Pavan Deolasee wrote:
> >
> > Currently each tuple is moved individually. You'd need to inspect the
> > whole HOT chain on a page, calculate space for that and then try to move
> > them all in one go. I was originally thinking that would be a problem,
> > but its not so bad - but it may cause us to end repair_frag() earlier
> > than we otherwise would depending upon the game of Tetris plays out.
> >
> >
> Umm.. I still need to look deeper to understand the VACUUM FULL code,
> but ISTM
> that we can move tuple chains just the way its done today, without
> bothering to keep
> HOT-update chains intact. The tuples may actually got into different
> pages and have
> equal number of index entries. To my mind, this is not such a big
> problem because
> we shouldn't expect too many HOT-update chains while running VACUUM FULL.
> Isn't that true ?

Well, its true enough to be a great argument.

So what you're saying is: we do nothing and it just works. At least not
too badly, and at very least: no worse than it does today.

[Oh dear! I just finished writing prototype of VACUUM FULL-with-reindex
when I read this, so either way it looks like nothing more needed on
this utility. 1 down, 3 to go.]

Simon Riggs

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