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Re: Page Checksums + Double Writes

From: Robert Haas <robertmhaas(at)gmail(dot)com>
To: Simon Riggs <simon(at)2ndquadrant(dot)com>
Cc: Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>, Kevin Grittner <Kevin(dot)Grittner(at)wicourts(dot)gov>, Alvaro Herrera <alvherre(at)commandprompt(dot)com>, David Fetter <david(at)fetter(dot)org>, Pg Hackers <pgsql-hackers(at)postgresql(dot)org>
Subject: Re: Page Checksums + Double Writes
Date: 2011-12-22 00:45:19
Message-ID: CA+TgmoYnof7WDBhTSvUBpOdD+0LGh0yfDX4Xmu6NsC6kNeSOcA@mail.gmail.com (view raw or flat)
Thread:
Lists: pgsql-hackers
On Wed, Dec 21, 2011 at 7:06 PM, Simon Riggs <simon(at)2ndquadrant(dot)com> wrote:
> My feeling is it probably depends upon how different the formats are,
> so given we are discussing a 4 byte addition to the header, it might
> be doable.

I agree.  When thinking back on Zoltan's patches, it's worth
remembering that he had a number of pretty bad ideas mixed in with the
good stuff - such as taking a bunch of things that are written as
macros for speed, and converting them to function calls.  Also, he
didn't make any attempt to isolate the places that needed to know
about both page versions; everybody knew about everything, everywhere,
and so everything needed to branch in places where it had not needed
to do so before.  I don't think we should infer from the failure of
those patches that no one can do any better.

On the other hand, I also agree with Tom that the chances of getting
this done in time for 9.2 are virtually zero, assuming that (1) we
wish to ship 9.2 in 2012 and (2) we don't wish to be making
destabilizing changes beyond the end of the last CommitFest.  There is
a lot of work here, and I would be astonished if we could wrap it all
up in the next month.  Or even the next four months.

--
Robert Haas
EnterpriseDB: http://www.enterprisedb.com
The Enterprise PostgreSQL Company

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