Re: Block-level CRC checks - Mailing list pgsql-hackers

From Richard Huxton
Subject Re: Block-level CRC checks
Date
Msg-id 4B159138.4060501@archonet.com
Whole thread Raw
In response to Re: Block-level CRC checks  (Bruce Momjian <bruce@momjian.us>)
Responses Re: Block-level CRC checks  (Greg Stark <gsstark@mit.edu>)
List 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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