On Fri, Apr 1, 2016 at 9:10 AM, Noah Misch <n...@leadboat.com> wrote: > On Thu, Mar 31, 2016 at 04:48:26PM +0900, Masahiko Sawada wrote: >> On Thu, Mar 31, 2016 at 2:02 PM, Noah Misch <n...@leadboat.com> wrote: >> > On Thu, Mar 10, 2016 at 01:04:11AM +0900, Masahiko Sawada wrote: >> >> As a result of looked into code around the recvoery, ISTM that the >> >> cause is related to relation cache clear. >> >> In heap_xlog_visible, if the standby server receives WAL record then >> >> relation cache is eventually cleared in vm_extend, but If standby >> >> server receives FPI then relation cache would not be cleared. >> >> For example, after I applied attached patch to HEAD, (it might not be >> >> right way but) this problem seems to be resolved. >> >> >> >> Is this a bug? or not? >> > >> > It's a bug. I don't expect it causes queries to return wrong answers, >> > because >> > visibilitymap.c says "it's always safe to clear a bit in the map from >> > correctness point of view." (The bug makes a visibility map bit >> > temporarily >> > appear to have been cleared.) I still call it a bug, because recovery >> > behavior becomes too difficult to verify when xlog replay produces >> > conditions >> > that don't happen outside of recovery. Even if there's no way to get a >> > wrong >> > query answer today, this would be too easy to break later. I wonder if we >> > make the same omission in other xlog replay functions. Similar omissions >> > may >> > cause wrong query answers, even if this particular one does not. >> > >> > Would you like to bisect for the commit, or at least the major release, at >> > which the bug first appeared? >> > >> > I wonder if your discovery has any relationship to this recently-reported >> > case >> > of insufficient smgr invalidation: >> > http://www.postgresql.org/message-id/flat/CAB7nPqSBFmh5cQjpRbFBp9Rkv1nF=nh2o1fxkkj6yvobtvy...@mail.gmail.com >> > >> >> I'm not sure this bug has relationship to another issue you mentioned >> but after further investigation, this bug seems to be reproduced even >> on more older version. >> At least I reproduced it at 9.0.0. > > Would you try PostgreSQL 9.2.16? The visibility map was not crash safe and > had no correctness implications until 9.2. If 9.2 behaves this way, it's > almost certainly not a recent regression.
Yeah, I reproduced it on 9.2.0 and 9.2.16, it's not recent regression. The commit is 503c7305a1e379f95649eef1a694d0c1dbdc674a which introduces crash-safe visibility map. Regards, -- Masahiko Sawada -- Sent via pgsql-hackers mailing list (pgsql-hackers@postgresql.org) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-hackers
