On 2021-Apr-08, Tom Lane wrote:
> Yeah. I hit this on another machine that isn't using EXEC_BACKEND,
> and I concur it looks more like a race condition. I think the problem
> is that autovacuum is calling find_all_inheritors() on a relation it
> has no lock on, contrary to that function's API spec. find_all_inheritors
> assumes the OID it's given is valid and locked, and adds it to the
> result list automatically. Then it looks for children, and won't find
> any in the race case where somebody else just dropped the table.
Hmm. Autovacuum tries hard to avoid grabbing locks on relations until
really needed (at vacuum/analyze time), which is why all these tests
only use data that can be found in the pg_class rows and pgstat entries.
So I tend to think that my initial instinct was the better direction: we
should not be doing any find_all_inheritors() here at all, but instead
rely on pg_class.reltuples to be set for the partitioned table.
I'll give that another look. Most places already assume that reltuples
isn't set for a partitioned table, so they shouldn't care. I wonder,
though, whether we should set relpages to some value other than 0 or -1.
(I'm inclined not to, since autovacuum does not use it.)
--
Álvaro Herrera Valdivia, Chile