Robert Haas <robertmh...@gmail.com> wrote: > On Sat, Nov 2, 2019 at 8:23 AM Antonin Houska <a...@cybertec.at> wrote: > > Change to hint bits does not result in LSN change in the case I described > > here > > > > https://www.postgresql.org/message-id/28452.1572443058%40antos > > > > but I consider this a bug (BTW, I discovered this problem when thinking > > about > > the use of LSN as encryption IV). Do you mean any other case? If LSN does > > not > > get changed, then the related full-page image WAL record is not guaranteed > > to > > be on disk during crash recovery. Thus if page checksum is invalid due to > > torn-page write, there's now WAL record to fix the page. > > I thought the idea was that the first change to hint bits after a > given checkpoint produced an FPI, but subsequent changes within the > same checkpoint cycle do not.
Got it, this is what happens in XLogSaveBufferForHint(). Perhaps we can fix it by issuing XLOG_NOOP record in the cases that produce no FPI. Of course only if the encryption is enabled. -- Antonin Houska Web: https://www.cybertec-postgresql.com
