Re: archive status ".ready" files may be created too early

On Fri, Dec 13, 2019 at 7:50 AM Bossart, Nathan <bossartn(at)amazon(dot)com> wrote:
>
> Hi hackers,
>
> I believe I've uncovered a bug that may cause archive status ".ready"
> files to be created too early, which in turn may cause an incorrect
> version of the corresponding WAL segment to be archived.
>
> The crux of the issue seems to be that XLogWrite() does not wait for
> the entire record to be written to disk before creating the ".ready"
> file. Instead, it just waits for the last page of the segment to be
> written before notifying the archiver. If PostgreSQL crashes before
> it is able to write the rest of the record, it will end up reusing the
> ".ready" segment at the end of crash recovery. In the meantime, the
> archiver process may have already processed the old version of the
> segment.

Maybe I'm missing something... But since XLogWrite() seems to
call issue_xlog_fsync() before XLogArchiveNotifySeg(), ISTM that
this trouble shouldn't happen. No?

Regards,

--
Fujii Masao