Eelke is almost certainly correct that your locking is blocking autovacuum. Autovacuum is designed to give way to user activity, deliberately. If those tables are locked, autovacuum cannot vacuum them.
For posterity, however, I wanted to give an example set of settings for hyper-aggressive autovacuum, since the settings you gave don't quite do it. Note that making autovacuum more aggressive is unlikely to solve your problem, however. Also note that the default autovacuum settings are based on running over 200 test runs using DBT2 seeking an optimal combination of settings, so the defaults should be assumed to be good unless you have a solid reason to think otherwise, or unless your database is significantly outside the mainstream for OLTP databases (e.g. a tiny database which gets 10K updates per second, or a 3TB data warehouse).
First, turn on logging so you can check up on whether autovacuum is doing what you think it is:
log_autovacuum_min_duration = 0
Then let's make more autovac workers and have them check tables more often:
autovacuum_max_workers = 6
autovacuum_naptime = 15s
Let's lower the thresholds for auto-vacuum and auto-analyze to trigger sooner:
autovacuum_vacuum_threshold = 25
autovacuum_vacuum_scale_factor = 0.1
autovacuum_analyze_threshold = 10
autovacuum_analyze_scale_factor = 0.05
Then let's make autovacuum less interruptable, so it completes faster, but at the cost of having a greater impact on concurrent user activity:
autovacuum_vacuum_cost_delay = 10ms
autovacuum_vacuum_cost_limit = 1000
There's your full program for generically aggressive autovacuum, which might be apppropriate for a small database getting a very high rate of updates, but might have too great of an impact on concurrent user activity.
Also, note that autovacuum parameters can be adjusted per table, which is almost always a better answer for needing to adjust autovacuum's behavior.
Again, though, it's unlikely to address your real problem.
To return space to the OS, use VACUUM FULL
. While being at it, I suppose you run VACUUM FULL ANALYZE
. I quote the manual:
FULL
Selects "full" vacuum, which can reclaim more space, but takes much
longer and exclusively locks the table. This method also requires
extra disk space, since it writes a new copy of the table and doesn't
release the old copy until the operation is complete. Usually this
should only be used when a significant amount of space needs to be
reclaimed from within the table.
Bold emphasis mine.
CLUSTER
achieves that, too, as a collateral effect.
Plain VACUUM
does not normally achieve your goal ("one or more pages at the end of a table entirely free"). It does not reorder rows and only prunes empty pages from the physical end of the file when the opportunity arises - like your quote from the manual instructs.
You can get empty pages at the end of the physical file when you INSERT
a batch of rows and DELETE
them before other tuples get appended. Or it can happen by coincidence if enough rows are deleted.
There are also special settings that might prevent VACUUM FULL
from reclaiming space. See:
Prepare empty pages at the end of a table for testing
The system column ctid
represents the physical position of a row. You need to understand that column:
We can work with that and prepare a table by deleting all rows from the last page:
DELETE FROM tbl t
USING (
SELECT (split_part(ctid::text, ',', 1) || ',0)')::tid AS min_tid
, (split_part(ctid::text, ',', 1) || ',65535)')::tid AS max_tid
FROM tbl
ORDER BY ctid DESC
LIMIT 1
) d
WHERE t.ctid BETWEEN d.min_tid AND d.max_tid;
Now, the last page is empty. This ignores concurrent writes. Either you are the only one writing to that table or you need to to take a write lock to avoid interference.
The query is optimized to identify qualifying rows quickly. The second number of a tid
is the tuple index stored as unsigned int2
, and 65535
is the maximum for that type (2^16 - 1
), so that's the safe upper bound.
SQL Fiddle (reusing a simple table from a different case.)
Tools to measure row / table size:
Disk full
You need wiggle room on disk for any of these operations. There is also the community tool pg_repack
as replacement for VACUUM FULL
/ CLUSTER
. It avoids exclusive locks but needs free space to work with as well. The manual:
Requires free disk space twice as large as the target table(s) and indexes.
As a last resort, you can run a dump/restore cycle. That removes all bloat from tables and indexes, too. Closely related question:
The answer over there is pretty radical. If your situation allows for it (no foreign keys or other references preventing row deletions), and no concurrent access to the table), you can just:
Dump the table to disk connecting from a remote computer with plenty of disk space (-a
for --data-only
):
From remote shell, dump table data:
pg_dump -h <host_name> -p <port> -t mytbl -a mydb > db_mytbl.sql
In a pg session, TRUNCATE
the table:
-- drop all indexes and constraints here for best performance
TRUNCATE mytbl;
From remote shell, restore to same table:
psql -h <host_name> -p <port> mydb -f db_mytbl.sql
-- recreate all indexes and constraints here
It is now free of any dead rows or bloat.
But maybe you can have that simpler?
Can you make enough space on disk by deleting (moving) unrelated files?
Can you VACUUM FULL
smaller tables first, one by one, thereby freeing up enough disk space?
Can you run REINDEX TABLE
or REINDEX INDEX
to free disk space from bloated indexes?
Whatever you do, don't be rash. If in doubt, backup everything to a secure location first.
Best Answer
The default settings will probably be fine.
That will limit the IO write usage to about 4MB/sec, that is,
4kB/msec = (8KB * vacuum_cost_limit / vacuum_cost_page_dirty / autovacuum_vacuum_cost_delay)
And RAM usage to about 48 MB
(autovacuum_max_workers * maintenance_work_mem)