| From: | Florian Weimer <fw(at)deneb(dot)enyo(dot)de> |
|---|---|
| To: | Greg Smith <greg(at)2ndQuadrant(dot)com> |
| Cc: | Heikki Linnakangas <hlinnakangas(at)vmware(dot)com>, Bruce Momjian <bruce(at)momjian(dot)us>, Daniel Farina <daniel(at)heroku(dot)com>, Jeff Davis <pgsql(at)j-davis(dot)com>, Simon Riggs <simon(at)2ndquadrant(dot)com>, PostgreSQL-development <pgsql-hackers(at)postgresql(dot)org>, Jim Nasby <jim(at)nasby(dot)net> |
| Subject: | Re: Enabling Checksums |
| Date: | 2013-04-18 17:04:41 |
| Message-ID: | 8738unrcra.fsf@mid.deneb.enyo.de |
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| Lists: | pgsql-hackers |
* Greg Smith:
> The TCP/IP checksum spec is at https://tools.ietf.org/html/rfc793 ;
> its error detection limitations are described at
> http://www.noahdavids.org/self_published/CRC_and_checksum.html ; and a
> good article about optimizing its code is at
> http://www.locklessinc.com/articles/tcp_checksum/ I'll take a longer
> look at whether it's an improvement on the Fletcher-16 used by the
> current patch.
The TCP checksum is too weak to be practical. Every now an then, I
see data transfers where the checksum is valid, but the content
contains bit flips. Anything that flips bits randomly at intervals
which are multiples of 16 bits is quite likely to pass through
checksum detection.
In practice, TCP relies on checksumming on the sub-IP layers.
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