On Fri, Jan 8, 2021 at 2:12 PM tsunakawa.ta...@fujitsu.com <tsunakawa.ta...@fujitsu.com> wrote: > > From: Robert Haas <robertmh...@gmail.com> > > Were the issues that I mentioned regarding GIST (and maybe other AMs) > > in the last paragraph of > > http://postgr.es/m/CA+TgmoZEZ5RONS49C7mEpjhjndqMQtVrz_LCQUkpRW > > dmrev...@mail.gmail.com > > addressed in some way? That seems like a pretty hard engineering > > problem to me, and I don't see that there's been any discussion of it. > > Those are correctness concerns separate from any wal_level tracking we > > might want to do to avoid accidental mistakes. > > Thank you very much for reminding me of this. I forgot I replied as follows: > > > -------------------------------------------------- > Unlogged GiST indexes use fake LSNs that are instance-wide. Unlogged > temporary GiST indexes use backend-local sequence values. Other unlogged and > temporary relations don't set LSNs on pages. So, I think it's enough to call > GetFakeLSNForUnloggedRel() when wal_level = none as well. > -------------------------------------------------- > > > But this is not correct. We have to allow (RM_GIST_ID, XLOG_GIST_ASSIGN_LSN) > WAL records to be emitted (by tweaking the filter in XLogInsert()), just like > those WAL records are emitted when wal_level = minimal and and other WAL > records are not emitted.
I think it's better to have index AM (and perhaps table AM) control it instead of filtering in XLogInsert(). Because otherwise third-party access methods that use LSN like gist indexes cannot write WAL records at all when wal_level = none even if they want. Regards, -- Masahiko Sawada EnterpriseDB: https://www.enterprisedb.com/
