Re: Why does VACUUM FULL pg_class sometimes wait for ShareLock on another transaction after getting AccessExclusiveLock on pg_class?

On Thu, Jul 22, 2021 at 5:08 PM Marcin Barczynski <
mbarczynski(at)starfishstorage(dot)com> wrote:

> On Thu, Jul 22, 2021 at 3:51 PM Laurenz Albe <laurenz(dot)albe(at)cybertec(dot)at>
> wrote:
> >
> > On Thu, 2021-07-22 at 12:55 +0200, Marcin Barczynski wrote:
> > > There was a long-running transaction consisting of two queries:
> > >
> > > CREATE TEMPORARY TABLE abc AS SELECT * FROM def_view;
> > > INSERT INTO xyz_table SELECT * FROM abc;
> > >
> > > When I ran VACUUM FULL pg_class, it waited for ShareLock on that
> transaction:
> >
> > There must have been something else using "pg_class", since the above
> > won't take any permament locks on "pg_class", nor should it block VACUUM.
>
>
> Thanks for your reply. I dugged a bit deeper, and it turned out that
> VACUUM FULL hung in heapam_index_build_range_scan.
> It's PostgreSQL 13.3. Comments around heapam_handler.c:1482:
>

What's more, running VACUUM FULL pg_class sometimes causes a deadlock with
transactions using temp tables. For example:

DETAIL: Process 6703 waits for ShareLock on transaction 108850229; blocked
by process 6591.
Process 6591 waits for AccessShareLock on relation 1259 of database
16517; blocked by process 6703.
Process 6703: VACUUM (FULL, VERBOSE, ANALYZE) pg_class
Process 6591: SELECT * FROM stored_procedure()

Isn't it a bug?
Is there any way to safely run VACUUM FULL pg_class?
My workload involves lots of temp tables, and I need to get rid of the
bloat regularly.

--
Regards,
Marcin Barczynski