On Tue, Nov 10, 2020 at 5:44 AM Michael Paquier <michael@paquier.xyz> wrote:
On Thu, Nov 05, 2020 at 10:57:16AM +0900, Michael Paquier wrote: > I was referring to the patch I sent on this thread that fixes the > detection of a corruption for the zero-only case and where pd_lsn > and/or pg_upper are trashed by a corruption of the page header. Both > cases allow a base backup to complete on HEAD, while sending pages > that could be corrupted, which is wrong. Once you make the page > verification rely only on pd_checksum, as the patch does because the > checksum is the only source of truth in the page header, corrupted > pages are correctly detected, causing pg_basebackup to complain as it > should. However, it has also the risk to cause pg_basebackup to fail > *and* to report as broken pages that are in the process of being > written, depending on how slow a disk is able to finish a 8kB write. > That's a different kind of wrongness, and users have two more reasons > to be pissed. Note that if a page is found as torn we have a > consistent page header, meaning that on HEAD the PageIsNew() and > PageGetLSN() would pass, but the checksum verification would fail as > the contents at the end of the page does not match the checksum.
Magnus, as the original committer of 4eb77d5, do you have an opinion to share?
I admit that I at some point lost track of the overlapping threads around this, and just figured there was enough different checksum-involved-people on those threads to handle it :) Meaning the short answer is "no, I don't really have one at this point".
Slightly longer comment is that it does seem reasonable, but I have not read in on all the different issues discussed over the whole thread, so take that as a weak-certainty comment.
