Re: autovacuum next steps, take 2

Tom Lane wrote:

> I think an absolute minimum requirement for a sane design is that no two
> workers ever try to vacuum the same table concurrently, and I don't see
> where that behavior will emerge from your proposal; whereas it's fairly
> easy to make it happen if non-first workers pay attention to what other
> workers are doing.

FWIW, I've always considered this to be a very important and obvious
issue, and I think I've neglected mentioning it (maybe I did too few
times).  But I think this is pretty easy to do, just have each worker
advertise the current table it's working on in shared memory, and add a
recheck loop on the table-pick algorithm (with appropriate grabs of the
autovacuum lwlock), to make sure no one starts to vacuum the same table
you're going to process, at the same time.

-- 
Alvaro Herrera                                http://www.CommandPrompt.com/
PostgreSQL Replication, Consulting, Custom Development, 24x7 support