From: | Ants Aasma <ants(at)cybertec(dot)at> |
---|---|
To: | Ants Aasma <ants(at)cybertec(dot)at> |
Cc: | Florian Pflug <fgp(at)phlo(dot)org>, Andres Freund <andres(at)2ndquadrant(dot)com>, Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>, Bruce Momjian <bruce(at)momjian(dot)us>, Jeff Davis <pgsql(at)j-davis(dot)com>, Heikki Linnakangas <hlinnakangas(at)vmware(dot)com>, Simon Riggs <simon(at)2ndquadrant(dot)com>, Greg Smith <greg(at)2ndquadrant(dot)com>, PostgreSQL-development <pgsql-hackers(at)postgresql(dot)org> |
Subject: | Re: Enabling Checksums |
Date: | 2013-04-18 18:02:49 |
Message-ID: | CA+CSw_tfmXkGz_AE+f+3y99b06XZwZ-N1+4a3DFB389OoL-bsQ@mail.gmail.com |
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Lists: | pgsql-hackers |
On Thu, Apr 18, 2013 at 8:24 PM, Ants Aasma <ants(at)cybertec(dot)at> wrote:
> On Thu, Apr 18, 2013 at 8:15 PM, Florian Pflug <fgp(at)phlo(dot)org> wrote:
>> So either the CRC32-C polynomial isn't irreducible, or there something
>> fishy going on. Could there be a bug in your CRC implementation? Maybe
>> a mixup between big and little endian, or something like that?
>
> I'm suspecting an implementation bug myself. I already checked the
> test harness and that was all sane, compiler hadn't taken any
> unforgivable liberties there. I will crosscheck the output with other
> implementations to verify that the checksum is implemented correctly.
Looks like the implementation is correct. I cross-referenced it
against a bitwise algorithm for crc32 with the castagnoli polynomial.
This also rules out any endianness issues as the bitwise variant
consumes input byte at a time.
What ever it is, it is something specific to PostgreSQL page layout.
If I use /dev/urandom as the source the issue disappears. So much for
CRC32 being proven good.
Regards,
Ants Aasma
--
Cybertec Schönig & Schönig GmbH
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A-2700 Wiener Neustadt
Web: http://www.postgresql-support.de
--
Cybertec Schönig & Schönig GmbH
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A-2700 Wiener Neustadt
Web: http://www.postgresql-support.de
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