Re: New CRC algorithm: Slicing by 8

On Mon, 2006-10-23 at 13:52 -0400, Tom Lane wrote:
> "Simon Riggs" <simon(at)2ndquadrant(dot)com> writes:
> > Instead, I'd like to include a parameter to turn off CRC altogether, for
> > heavily CPU bound operations and the WAL drive on trustworthy hardware.
>
> No can do --- we rely on the checksums to be able to tell when we've hit
> the end of WAL during replay.

No we don't: Zero length records are the trigger for EOF.

Sure, a CRC failure will cause replay to end, but only if you calculate
it and compare it to whats on disk - which is the bit I would turn off.
We don't rely on that, however, so it is avoidable.

In most cases, it would be foolish to avoid: but there are cases where
the data is CRC checked by the hardware/system already, so I'd like to
make an option to turn this off, defaulting to on, for safety.

> You may as well propose not writing WAL
> at all (and no, I don't think it'd pass).

That would undo all of my efforts, so no I wouldn't consider that.

--
Simon Riggs
EnterpriseDB http://www.enterprisedb.com