On Wed, Jan 17, 2024 at 3:58 PM Robert Haas <robertmh...@gmail.com> wrote: > > Ah, I realize I was not clear. I am now talking about inconsistencies > > in vacuuming the FSM itself. FreeSpaceMapVacuumRange(). Not updating > > the freespace map during the course of vacuuming the heap relation. > > Fair enough, but I'm still not quite sure exactly what the question > is. It looks to me like the current code, when there are indexes, > vacuums the FSM after each round of index vacuuming. When there are no > indexes, doing it after each round of index vacuuming would mean never > doing it, so instead we vacuum the FSM every ~8GB. I assume what > happened here is that somebody decided doing it after each round of > index vacuuming was the "right thing," and then realized that was not > going to work if no index vacuuming was happening, and so inserted the > 8GB threshold to cover that case.
Note that VACUUM_FSM_EVERY_PAGES is applied against the number of rel_pages "processed" so far -- *including* any pages that were skipped using the visibility map. It would make a bit more sense if it was applied against scanned_pages instead (just like FAILSAFE_EVERY_PAGES has been since commit 07eef53955). In other words, VACUUM_FSM_EVERY_PAGES is applied against a thing that has only a very loose relationship with physical work performed/time elapsed. I tend to suspect that VACUUM_FSM_EVERY_PAGES is fundamentally the wrong idea. If it's such a good idea then why not apply it all the time? That is, why not apply it independently of whether nindexes==0 in the current VACUUM operation? (You know, just like with FAILSAFE_EVERY_PAGES.) -- Peter Geoghegan
