On 08/02/2016 02:33 PM, Bruce Momjian wrote:
> My guess is that the bytes are there to detect problems where
> a 512-byte disk sector is zeroed by a disk failure.
Does that seem plausible? (a) there is only one such header for
every 16 512-byte disk sectors, so it only affords a 6% chance of
detecting a zeroed sector, and (b) the header contains other
non-zero values in fields other than xlp_pageaddr, so the use
of a fixed value for _that field_ in zeroed tail blocks would
not prevent (or even reduce the 6% probability of) detecting
a sector zeroed by a defect.
-Chap
