Re: max_fsm_pages

Ryan Mahoney <ryan(at)paymentalliance(dot)net> writes:
> When interactively calculating the ideal value for max_fsm_pages by
> summarizing the output of VACUUM VERBOSE, which statistic from vacuum am
> I concerned with?

7.4 will tell you exactly how many FSM slots you need:

foo=# vacuum verbose;
...
INFO: free space map: 246 relations, 464 pages stored; 4160 total pages needed
DETAIL: Allocated FSM size: 1000 relations + 20000 pages = 178 kB shared memory.
VACUUM

In this example, the minimum FSM settings to not discard any data would
be max_fsm_relations = 246, max_fsm_pages = 4160. Note that you need to
have vacuumed all databases fairly recently for the totals to be really
trustworthy.

In previous versions you're kind of on your own :-(

regards, tom lane