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Re: Page-level version upgrade (was: Block-level CRC checks)

From: Bruce Momjian <bruce(at)momjian(dot)us>
To: Robert Haas <robertmhaas(at)gmail(dot)com>
Cc: Greg Stark <gsstark(at)mit(dot)edu>, decibel <decibel(at)decibel(dot)org>, Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>, Simon Riggs <simon(at)2ndquadrant(dot)com>, Heikki Linnakangas <heikki(dot)linnakangas(at)enterprisedb(dot)com>, Aidan Van Dyk <aidan(at)highrise(dot)ca>, Alvaro Herrera <alvherre(at)commandprompt(dot)com>, Pg Hackers <pgsql-hackers(at)postgresql(dot)org>
Subject: Re: Page-level version upgrade (was: Block-level CRC checks)
Date: 2009-12-02 02:31:20
Message-ID: (view raw, whole thread or download thread mbox)
Lists: pgsql-hackers
Robert Haas wrote:
> On Tue, Dec 1, 2009 at 5:15 PM, Greg Stark <gsstark(at)mit(dot)edu> wrote:
> > On Tue, Dec 1, 2009 at 9:58 PM, decibel <decibel(at)decibel(dot)org> wrote:
> >> What happened to the work that was being done to allow a page to be upgraded
> >> on the fly when it was read in from disk?
> >
> > There were no page level changes between 8.3 and 8.4.
> That's true, but I don't think it's the full and complete answer to
> the question.  Zdenek submitted a page for CF 2008-11 which attempted
> to add support for multiple page versions.  I guess we're on v4 right
> now, and he was attempting to add support for v3 pages, which would
> have allowed reading in pages from old PG versions.  To put it
> bluntly, the code wasn't anything I would have wanted to deploy, but
> the reason why Zdenek gave up on fixing it was because several
> community members considerably senior to myself provided negative
> feedback on the concept.

Well, there were quite a number of open issues relating to page

	o  Do we write the old version or just convert on read?
	o  How do we write pages that get larger on conversion to the
	   new format?

As I rember the patch allowed read/wite of old versions, which greatly
increased its code impact.

  Bruce Momjian  <bruce(at)momjian(dot)us>

  + If your life is a hard drive, Christ can be your backup. +

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