| From: | Martijn van Oosterhout <kleptog(at)svana(dot)org> |
|---|---|
| To: | Gregory Stark <stark(at)enterprisedb(dot)com> |
| Cc: | Alvaro Herrera <alvherre(at)commandprompt(dot)com>, Zdenek Kotala <Zdenek(dot)Kotala(at)Sun(dot)COM>, Pg Hackers <pgsql-hackers(at)postgresql(dot)org> |
| Subject: | Re: Block-level CRC checks |
| Date: | 2008-10-30 18:34:26 |
| Message-ID: | 20081030183426.GB21451@svana.org |
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| Lists: | pgsql-hackers |
On Thu, Oct 30, 2008 at 03:41:17PM +0000, Gregory Stark wrote:
> The CRC is chosen such that if you CRC the resulting packet including the CRC
> you get a CRC of 0. That can be done for whatever offset the CRC appears at I
> believe.
IIRC, you calculate the CRC-32 of the page, then XOR it over where it's
supposed to end up. No need to preseed (or more accurately, it doesn't
matter how you preseed, the result is the same).
For checking it doesn't matter either, just checksum the page and if
you get zero it's correct.
Have a nice day,
--
Martijn van Oosterhout <kleptog(at)svana(dot)org> http://svana.org/kleptog/
> Please line up in a tree and maintain the heap invariant while
> boarding. Thank you for flying nlogn airlines.
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