Performance of autovacuum and full vacuum of database

Hi Forum,

Should autovacuum reclaim most of the free space of a database? We are
trying to configure our database and running pg_autovacuum to streamline our
database. We have increased the max_fsm_pages to a value larger than the
total pages needed (see the output from a full vacuum bellow "LAST FEW LINES
OF FULL VACUUM") and turned on pg_autovacuum.

Nevertheless, it seems that a full vacuum that we run at night finds a lot
of free space (see "EXCERPT FROM THE FULL VACUUM TO SHOW THE VACUUM OF ONE
TABLE"). I would have expected that with the configuration of our database
and with autovacuum working during the day, the amount of space that a full
vacuum would find would be minimal.

We are running pg_autovacuum with its defaults parameters. I can see that
autovacuum is working because the CPU utilization for the autovacuum PID
goes up every five minutes or so and then it goes down to almost nothing.

LAST FEW LINES OF FULL VACUUM

INFO: free space map: 483 relations, 219546 pages stored; 153104 total
pages needed

DETAIL: Allocated FSM size: 1000 relations + 170000 pages = 1057 kB shared
memory.

EXCERPT FROM THE FULL VACUUM TO SHOW THE VACUUM OF ONE TABLE

INFO: "en0029": found 66035 removable, 1310162 nonremovable row versions in
417

87 pages

DETAIL: 0 dead row versions cannot be removed yet.

Nonremovable row versions range from 233 to 1165 bytes long.

There were 1746 unused item pointers.

Total free space (including removable row versions) is 20825932 bytes.

1453 pages are or will become empty, including 0 at the end of the table.

2345 pages containing 16260040 free bytes are potential move destinations.

CPU 2.20s/0.22u sec elapsed 62.59 sec.