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Re: Block-level CRC checks

From: Richard Huxton <dev(at)archonet(dot)com>
To: Bruce Momjian <bruce(at)momjian(dot)us>
Cc: 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: Block-level CRC checks
Date: 2009-12-01 21:57:12
Message-ID: (view raw, whole thread or download thread mbox)
Lists: pgsql-hackers
Bruce Momjian wrote:
> Tom Lane wrote:
>> The suggestions that were made upthread about moving the hint bits
>> could resolve the second objection, but once you do that you might
>> as well just exclude them from the CRC and eliminate the guessing.
> OK, crazy idea #3.  What if we had a per-page counter of the number of
> hint bits set --- that way, we would only consider a CRC check failure
> to be corruption if the count matched the hint bit count on the page.

Can I piggy-back on Bruce's crazy idea and ask a stupid question?

Why are we writing out the hint bits to disk anyway? Is it really so
slow to calculate them on read + cache them that it's worth all this
trouble? Are they not also to blame for the "write my import data twice"

  Richard Huxton
  Archonet Ltd

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