On Tue, Oct 31, 2017 at 6:17 PM, Alexander Korotkov <a.korot...@postgrespro.ru> wrote: > On Tue, Oct 31, 2017 at 5:16 AM, Masahiko Sawada <sawada.m...@gmail.com> > wrote: >> >> On Mon, Oct 30, 2017 at 10:16 PM, Robert Haas <robertmh...@gmail.com> >> wrote: >> > On Tue, Oct 24, 2017 at 1:26 PM, Ivan Kartyshov >> > <i.kartys...@postgrespro.ru> wrote: >> >> Hello. I made some bugfixes and rewrite the patch. >> > >> > I don't think it's a good idea to deliberately leave the state of the >> > standby different from the state of the master on the theory that it >> > won't matter. I feel like that's something that's likely to come back >> > to bite us. >> >> I agree with Robert. What happen if we intentionally don't apply the >> truncation WAL and switched over? If we insert a tuple on the new >> master server to a block that has been truncated on the old master, >> the WAL apply on the new standby will fail? I guess there are such >> corner cases causing failures of WAL replay after switch-over. > > > Yes, that looks dangerous. One approach to cope that could be teaching heap > redo function to handle such these situations. But I expect this approach > to be criticized for bad design. And I understand fairness of this > criticism. > > However, from user prospective of view, current behavior of > hot_standby_feedback is just broken, because it both increases bloat and > doesn't guarantee that read-only query on standby wouldn't be cancelled > because of vacuum. Therefore, we should be looking for solution: if one > approach isn't good enough, then we should look for another approach. > > I can propose following alternative approach: teach read-only queries on hot > standby to tolerate concurrent relation truncation. Therefore, when > non-existent heap page is accessed on hot standby, we can know that it was > deleted by concurrent truncation and should be assumed to be empty. Any > thoughts? >
You also meant that the applying WAL for AccessExclusiveLock is always skipped on standby servers to allow scans to access the relation? Regards, -- Masahiko Sawada NIPPON TELEGRAPH AND TELEPHONE CORPORATION NTT Open Source Software Center -- Sent via pgsql-hackers mailing list (pgsql-hackers@postgresql.org) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-hackers
