From: | Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> |
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To: | "Robert Haas" <robertmhaas(at)gmail(dot)com> |
Cc: | "Heikki Linnakangas" <heikki(dot)linnakangas(at)enterprisedb(dot)com>, "Zdenek Kotala" <Zdenek(dot)Kotala(at)sun(dot)com>, PostgreSQL-development <pgsql-hackers(at)postgresql(dot)org> |
Subject: | Re: [WIP] In-place upgrade |
Date: | 2008-11-04 16:14:11 |
Message-ID: | 20742.1225815251@sss.pgh.pa.us |
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"Robert Haas" <robertmhaas(at)gmail(dot)com> writes:
> Well, I just proposed an approach that doesn't work this way, so I
> guess I'll have to put myself in the disagree category, or anyway yet
> to be convinced. As long as you can move individual tuples onto new
> pages, you can eventually empty V3 pages and reinitialize them as new,
> empty V4 pages. You can force that process along via, say, VACUUM,
> but in the meantime you can still continue to read the old pages
> without being forced to change them to the new format. That's not the
> only possible approach, but it's not obvious to me that it's insane.
> If you think it's a non-starter, it would be good to know why.
That's sane *if* you can guarantee that only negligible overhead is
added for accessing data that is in the up-to-date format. I don't
think that will be the case if we start putting version checks into
every tuple access macro.
regards, tom lane
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