fsm allocation

Hi

I manage a moderately large database (version 8.0.4) that experiences
about 500 inserts per hour spread over a half dozen tables. Not many updates or deletions
(usually).

My problem involves fsm allocation and the vacuum utility.

Recently, I vacuumed and the output told me I had 47 relations, 151751
pages stored, and that I needed 237680 total pages. My fsm allocation
was for 1000 relations, 150000 pages.

I took this to mean the vacuum didn't work and that I needed to allocate
more pages. So I edited the conf file to allocate 300000 pages. After
altering SHMMAX on my system, I was able to restart the database.

I tried vacuuming again. This time, the output said I had 47
relations, 301906 pages and that I now needed 333104 total pages.

I'm confused. Does this mean I need to bump up my fsm allocation again?

By the way, what exactly is the 'free map space' anyway? And why does
it need so much space?

As always, your help is greatly appreciated.