On Sat, 2012-11-10 at 14:46 +0100, Florian Pflug wrote:
> > The bit indicating that a checksum is present may be lost due to
> > corruption.
>
> Though that concern mostly goes away if instead of a separate bit we use a
> special checksum value, say 0xDEAD, to indicate that the page isn't
> checksummed, no?
Right. But then we have an upgrade impact to set the checksum to 0xDEAD
on all existing pages, which seems to eliminate most of the possible
reason for it.
Also, we'd need to tweak the algorithm to make sure that it never landed
on that magic value. So if we think we might want this in the future, we
should reserve that magic value now.
But I can't think of many reasons for it, unless we expect people to be
turning checksums on and off repeatedly.
Regards,Jeff Davis