Heikki Linnakangas <heikki.linnakan...@enterprisedb.com> writes: > Can we get away with not setting the LSN on the heap page, even though > we set the PD_ALL_VISIBLE flag? If we don't set the LSN, the heap page > can be flushed to disk before the WAL record, but I think that's fine > because it's OK to have the flag set in the heap page even if the VM bit > is not set.
Why is that fine? It's certainly not fine from the standpoint of someone wondering why his index-only scan performs so badly. I think all this hair-splitting about cases where it's okay to have one bit set and not the other is misguided. To me, crash-safety of the VM means that its copy of the page-header bit is right. Period. Yes, it will cost something to ensure that; so what? If we don't get more than enough compensating performance gain from index-only scans, the whole patch is going to end up reverted. regards, tom lane -- Sent via pgsql-hackers mailing list (pgsql-hackers@postgresql.org) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-hackers