Re: Decoupling antiwraparound autovacuum from special rules around auto cancellation

On Thu, Dec 29, 2022 at 7:01 PM Peter Geoghegan <pg(at)bowt(dot)ie> wrote:
> Attached is v2, which is just to fix bitrot.

Attached is v3. We no longer apply vacuum_failsafe_age when
determining the cutoff for antiwraparound autovacuuming -- the new
approach is a bit simpler.

This is a fairly small change overall. Now any "table age driven"
autovacuum will also be antiwraparound when its
relfrozenxid/relminmxid attains an age that's either double the
relevant setting (either autovacuum_freeze_max_age or
effective_multixact_freeze_max_age), or 1 billion XIDs/MXIDs --
whichever is less.

That makes it completely impossible to disable antiwraparound
protections (the special antiwrap autocancellation behavior) for
table-age-driven autovacuums once table age exceeds 1 billion
XIDs/MXIDs. It's still possible to increase autovacuum_freeze_max_age
to well over a billion, of course. It just won't be possible to do
that while also avoiding the no-auto-cancellation behavior for those
autovacuums that are triggered due to table age crossing the
autovacuum_freeze_max_age/effective_multixact_freeze_max_age
threshold.

--
Peter Geoghegan