Re: Proposed WAL changes

On Wed, Mar 07, 2001 at 11:09:25AM -0500, Tom Lane wrote:
> "Vadim Mikheev" <vmikheev(at)sectorbase(dot)com> writes:
> >> * Store two past checkpoint locations, not just one, in pg_control.
> >> On startup, we fall back to the older checkpoint if the newer one
> >> is unreadable. Also, a physical copy of the newest checkpoint record
>
> > And what to do if older one is unreadable too?
> > (Isn't it like using 2 x CRC32 instead of CRC64 ? -:))
>
> Then you lose --- but two checkpoints gives you twice the chance of
> recovery (probably more, actually, since it's much more likely that
> the previous checkpoint will have reached disk safely).

Actually far more: if the checkpoints are minutes apart, even the
worst disk drive will certainly have flushed any blocks written for
the earlier checkpoint.

--
Nathan Myers
ncm(at)zembu(dot)com