> A disk-block CRC would detect partially written blocks (ie, power drops
> after disk has written M of the N sectors in a block). The disk's own
> checks will NOT consider this condition a failure.
But physical log recovery will rewrite every page that was changed
after last checkpoint, thus this is not an issue anymore.
> I'm not convinced
> that WAL will reliably detect it either (Vadim?). Certainly WAL will
> not help for corruption caused by external agents, away from any updates
> that are actually being performed/logged.
The external agent (if malvolent) could write a correct CRC anyway.
If on the other hand the agent writes complete garbage, vacuum will notice.
Andreas