What concerns me is that once the size has grown, even a VACUUM FULL
doesn't recover the space. Regular external VACUUMs keep the table at
around 10MB but if I use autovacuum and it grows to 40MB, a VACUUM FULL
will only get it down to 35MB. Is it possible that a canceled autovacuum
could result in permanently lost space?
AFAIK it should not. Can you also post VACUUM FULL VERBOSE output ?
I have attached the vacuum output below, along with the table definition
and a before and after of the table size. In this case a full vacuum (on
the 20000 row table) took it down from 34MB to 21MB. Maybe you can tell
me if this is reasonable, bearing in mind that after inserting 20000
rows at the start the size is about 6MB, and under normal vacuuming
conditions it sits around 10-12MB. This is better than the last time I
ran it though.
Thanks for the help,
Stuart
metadb=> \d test.transactions
Table "test.transactions"
Column | Type | Modifiers
-----------------+--------------------------------+-----------------------------------------------------------------------------
transaction_key | bigint | not null default nextval('test.transactions_transaction_key_seq'::regclass)
time | timestamp(6) without time zone | not null
cashier | text | not null
till | integer | not null
ring | integer | not null
ev_tstamp | integer | not null
ev_id | integer | not null
camera | integer | not null
Indexes:
"transactions_pkey" PRIMARY KEY, btree (transaction_key)
"transactions_camera_index" btree (camera)
"transactions_cashier_index" btree (cashier, transaction_key)
"transactions_event_index" btree (ring, ev_tstamp, ev_id)
"transactions_time_index" btree ("time", transaction_key)
metadb=> select pg_total_relation_size('test.transactions');
pg_total_relation_size
------------------------
34242560
(1 row)
metadb=> vacuum full verbose test.transactions;
INFO: vacuuming "test.transactions"
INFO: "transactions": found 0 removable, 19996 nonremovable row versions in 1592 pages
DETAIL: 0 dead row versions cannot be removed yet.
Nonremovable row versions range from 64 to 68 bytes long.
There were 2109 unused item pointers.
Total free space (including removable row versions) is 10199944 bytes.
1416 pages are or will become empty, including 0 at the end of the table.
1347 pages containing 10194740 free bytes are potential move destinations.
CPU 0.00s/0.01u sec elapsed 0.24 sec.
INFO: index "transactions_pkey" now contains 19996 row versions in 100 pages
DETAIL: 0 index row versions were removed.
42 index pages have been deleted, 42 are currently reusable.
CPU 0.00s/0.00u sec elapsed 0.00 sec.
INFO: index "transactions_event_index" now contains 19996 row versions in 215 pages
DETAIL: 0 index row versions were removed.
93 index pages have been deleted, 93 are currently reusable.
CPU 0.00s/0.00u sec elapsed 0.05 sec.
INFO: index "transactions_camera_index" now contains 19996 row versions in 146 pages
DETAIL: 0 index row versions were removed.
56 index pages have been deleted, 56 are currently reusable.
CPU 0.00s/0.00u sec elapsed 0.02 sec.
INFO: index "transactions_cashier_index" now contains 19996 row versions in 429 pages
DETAIL: 0 index row versions were removed.
290 index pages have been deleted, 290 are currently reusable.
CPU 0.00s/0.00u sec elapsed 0.05 sec.
INFO: index "transactions_time_index" now contains 19996 row versions in 1496 pages
DETAIL: 115518 index row versions were removed.
1412 index pages have been deleted, 1412 are currently reusable.
CPU 0.00s/0.11u sec elapsed 4.28 sec.
INFO: "transactions": moved 19996 row versions, truncated 1592 to 208 pages
DETAIL: CPU 0.12s/0.73u sec elapsed 20.75 sec.
INFO: index "transactions_pkey" now contains 19996 row versions in 112 pages
DETAIL: 19996 index row versions were removed.
0 index pages have been deleted, 0 are currently reusable.
CPU 0.00s/0.00u sec elapsed 0.06 sec.
INFO: index "transactions_event_index" now contains 19996 row versions in 215 pages
DETAIL: 19996 index row versions were removed.
77 index pages have been deleted, 77 are currently reusable.
CPU 0.00s/0.01u sec elapsed 0.04 sec.
INFO: index "transactions_camera_index" now contains 19996 row versions in 152 pages
DETAIL: 19996 index row versions were removed.
58 index pages have been deleted, 58 are currently reusable.
CPU 0.00s/0.00u sec elapsed 0.12 sec.
INFO: index "transactions_cashier_index" now contains 19996 row versions in 429 pages
DETAIL: 19996 index row versions were removed.
273 index pages have been deleted, 273 are currently reusable.
CPU 0.00s/0.01u sec elapsed 0.13 sec.
INFO: index "transactions_time_index" now contains 19996 row versions in 1496 pages
DETAIL: 19996 index row versions were removed.
1339 index pages have been deleted, 1339 are currently reusable.
CPU 0.00s/0.01u sec elapsed 0.30 sec.
INFO: vacuuming "pg_toast.pg_toast_18356"
INFO: "pg_toast_18356": found 0 removable, 0 nonremovable row versions in 0 pages
DETAIL: 0 dead row versions cannot be removed yet.
Nonremovable row versions range from 0 to 0 bytes long.
There were 0 unused item pointers.
Total free space (including removable row versions) is 0 bytes.
0 pages are or will become empty, including 0 at the end of the table.
0 pages containing 0 free bytes are potential move destinations.
CPU 0.00s/0.00u sec elapsed 0.00 sec.
INFO: index "pg_toast_18356_index" now contains 0 row versions in 1 pages
DETAIL: 0 index pages have been deleted, 0 are currently reusable.
CPU 0.00s/0.00u sec elapsed 0.00 sec.
VACUUM
metadb=> select pg_total_relation_size('test.transactions');
pg_total_relation_size
------------------------
21405696
(1 row)
---------------------------(end of broadcast)---------------------------
TIP 6: explain analyze is your friend
