Re: Autovacuum deadlock - bug or not?

"Mikael Carneholm" <Mikael(dot)Carneholm(at)WirelessCar(dot)com> writes:
> dfol=> select pgc.oid, pgc.relname from pg_class pgc where pgc.oid in (68950, 68122);
> oid | relname
> -------+--------------------------
> 68950 | vehicle_unit_data_200407
> 68122 | vehicle_unit_data_200301

> NOTICE: Clustering idx_vehicle_unit_data_200407_person_information__id on vehicle_unit_data_200407
> ERROR: deadlock detected
> DETAIL: Process 29022 waits for AccessExclusiveLock on relation 68950 of database 16390; blocked by process 15865.
> Process 15865 waits for AccessShareLock on relation 68122 of database 16390; blocked by process 29022.

> So it seems that it was the clustering of idx_vehicle_unit_data_200407_person_information__id on vehicle_unit_data_200407 that caused the deadlock.

Hmm, the CLUSTER on vehicle_unit_data_200407 wouldn't have taken any
lock on vehicle_unit_data_200301. Were you perhaps issuing a series
of CLUSTERs inside a transaction block? That would pile up exclusive
locks on all the tables involved, which is certainly deadlock-prone.

I'm also wondering where that NOTICE "Clustering ..." came from, because
there is no such message anywhere in the 8.1 PG sources. You *sure*
this is 8.1?

There's something funny about 15865 too; you said that was an autovacuum
process but I don't think so. VACUUM doesn't take AccessShareLock;
there's a different lock type that that tries to acquire. And it
doesn't take any locks at all on more than one user table at a time.

regards, tom lane