Couple of thing here:
1) Just because autovacuum is running, doesn't mean that it has actually
tried to vacuum a table. 5 minutes is the time that it sleeps in between
investigating activity to see if a vacuum is needed. If you want to see
if pg_autovacuum has actually tried to do anything you should up the the
logging with a -d2 switch on the pg_autovacuum command line.
2) pg_autovacuum only performs normal VACUUM commands, not VACUUM FULL.
As such, there will usually be some freespace left in the table. This is
not a bad thing as normal table activity will usually result in that
free space being reused, and it can be faster when it can use existing
free space rather than having to add space to the end off a table.
Matt
Carlos Oliva wrote:
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.
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TIP 5: don't forget to increase your free space map settings
