| 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: | 4B159138.4060501@archonet.com |
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| 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"
feature?
--
Richard Huxton
Archonet Ltd
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