VACUUM and fsm_max_pages

Good morning List,

I have seen several posts on this concept but I don’t find a complete
response.
I’m using BenchmarkSQL to evaluate PostgreSQL in transaction processing
and I work with PostgreSQL 8.1.3 on RHEL4-AS, Itanium-2 processor, 8GB RAM.

The database, generated via BenchmarkSQL and used, is a 200-warehouses
database and its size is about 20GB. The parameter “max_fsm_pages” is
equal to 20000 and “max_fsm_relations” to 1000.

Between two benchs, I launch a VACUUM but at the end of it, I see that
PostgreSQL asks me to increase the “max_fsm_pages” parameters and the
value proposed grows with the number of VACUUM launched…

Could someone explain me why ?

This is an example of the message I have :
Free space map contains 20576 pages in 17 relations
A total of 20000 page slots are in use (including overhead)
128512 page slots are required to track all free space
Current limits are : 20000 page slots, 1000 relations, using 223 KB
Number of page slots needed (128512) exceeds max_fsm_pages (20000)
HINT : Consider increasing the config parameter “max_fsm_pages” to a
value over 128512.

In order not to launch a VACUUM FULL, I increase the value of
“max_fsm_pages” but is it correct ?

Thank you for your help.
Regards,
Alexandra DANTE