Re: pg_autovacuum is nice ... but ...

"Marc G. Fournier" <scrappy(at)postgresql(dot)org> writes:
> Here is a vacuum verbose on gborg's database:

> INFO: free space map: 1000 relations, 7454 pages stored; 23072 total pages needed
> DETAIL: Allocated FSM size: 1000 relations + 20000 pages = 178 kB shared memory.
> and this is portal:

> INFO: free space map: 1000 relations, 7425 pages stored; 23024 total pages needed
> DETAIL: Allocated FSM size: 1000 relations + 20000 pages = 178 kB shared memory.

> so, you tell me ... should I increase them?

Yup. 20000 < 23072, so you're losing some proportion of FSM entries.
What's worse, the FSM relation table is maxed out (1000 = 1000) which
suggests that there are relations not being tracked at all; you have
no idea how much space is getting leaked in those.

You can determine the number of relations potentially needing FSM
entries by
select count(*) from pg_class where relkind in ('r','i','t');
--- sum over all databases in the cluster to get the right result.

Once you've fixed max_fsm_relations, do vacuums in all databases, and
then vacuum verbose should give you a usable lower bound for
max_fsm_pages.

regards, tom lane