Re: Enabling Checksums

On Mon, 2013-03-04 at 11:52 +0800, Craig Ringer wrote:
> I also suspect that at least in the first release it might be desirable
> to have an option that essentially says "something's gone horribly wrong
> and we no longer want to check or write checksums, we want a
> non-checksummed DB that can still read our data from before we turned
> checksumming off". Essentially, a way for someone who's trying
> checksumming in production after their staging tests worked out OK to
> abort and go back to the non-checksummed case without having to do a
> full dump and reload.

A recovery option to extract data sounds like a good idea, but I don't
want to go as far as you are suggesting here.

An option to ignore checksum failures (while still printing the
warnings) sounds like all we need here. I think Greg's point that the
page might be written out again (hiding the corruption) is a very good
one, but the same is true for zero_damaged_pages. So we can just still
allow the writes to proceed (including setting the checksum on write),
and the system should be as available as it would be without checksums.

Regards,
	Jeff Davis