1VACUUM() SQL Commands VACUUM()
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6 VACUUM - garbage-collect and optionally analyze a database
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10 VACUUM [ FULL ] [ FREEZE ] [ VERBOSE ] [ table ]
11 VACUUM [ FULL ] [ FREEZE ] [ VERBOSE ] ANALYZE [ table [ (column [, ...] ) ] ]
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15 VACUUM reclaims storage occupied by deleted tuples. In normal Post‐
16 greSQL operation, tuples that are deleted or obsoleted by an update are
17 not physically removed from their table; they remain present until a
18 VACUUM is done. Therefore it's necessary to do VACUUM periodically,
19 especially on frequently-updated tables.
20 With no parameter, VACUUM processes every table in the current data‐
22 base. With a parameter, VACUUM processes only that table.
23 VACUUM ANALYZE performs a VACUUM and then an ANALYZE for each selected
25 table. This is a handy combination form for routine maintenance
26 scripts. See ANALYZE [analyze(7)] for more details about its process‐
27 ing.
28 Plain VACUUM (without FULL) simply reclaims space and makes it avail‐
30 able for re-use. This form of the command can operate in parallel with
31 normal reading and writing of the table, as an exclusive lock is not
32 obtained. VACUUM FULL does more extensive processing, including moving
33 of tuples across blocks to try to compact the table to the minimum num‐
34 ber of disk blocks. This form is much slower and requires an exclusive
35 lock on each table while it is being processed.
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38 FULL Selects ``full'' vacuum, which may reclaim more space, but takes
39 much longer and exclusively locks the table.
40 FREEZE Selects aggressive ``freezing'' of tuples. Specifying FREEZE is
42 equivalent to performing VACUUM with the vacuum_freeze_min_age
43 parameter set to zero. The FREEZE option is deprecated and will
44 be removed in a future release; set the parameter instead.
45 VERBOSE
47 Prints a detailed vacuum activity report for each table.
48 ANALYZE
50 Updates statistics used by the planner to determine the most
51 efficient way to execute a query.
52 table The name (optionally schema-qualified) of a specific table to
54 vacuum. Defaults to all tables in the current database.
55 column The name of a specific column to analyze. Defaults to all col‐
57 umns.
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60 When VERBOSE is specified, VACUUM emits progress messages to indicate
61 which table is currently being processed. Various statistics about the
62 tables are printed as well.
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65 VACUUM cannot be executed inside a transaction block.
66 We recommend that active production databases be vacuumed frequently
68 (at least nightly), in order to remove expired rows. After adding or
69 deleting a large number of rows, it may be a good idea to issue a VAC‐
70 UUM ANALYZE command for the affected table. This will update the system
71 catalogs with the results of all recent changes, and allow the Post‐
72 greSQL query planner to make better choices in planning queries.
73 The FULL option is not recommended for routine use, but may be useful
75 in special cases. An example is when you have deleted most of the rows
76 in a table and would like the table to physically shrink to occupy less
77 disk space. VACUUM FULL will usually shrink the table more than a plain
78 VACUUM would. The FULL option does not shrink indexes; a periodic
79 REINDEX is still recommended. In fact, it is often faster to drop all
80 indexes, VACUUM FULL, and recreate the indexes.
81 VACUUM causes a substantial increase in I/O traffic, which can cause
83 poor performance for other active sessions. Therefore, it is sometimes
84 advisable to use the cost-based vacuum delay feature. See in the docu‐
85 mentation for details.
86 PostgreSQL includes an ``autovacuum'' facility which can automate rou‐
88 tine vacuum maintenance. For more information about automatic and man‐
89 ual vacuuming, see in the documentation.
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92 The following is an example from running VACUUM on a table in the
93 regression database:
94 regression=# VACUUM VERBOSE ANALYZE onek;
96 INFO: vacuuming "public.onek"
97 INFO: index "onek_unique1" now contains 1000 tuples in 14 pages
98 DETAIL: 3000 index tuples were removed.
99 0 index pages have been deleted, 0 are currently reusable.
100 CPU 0.01s/0.08u sec elapsed 0.18 sec.
101 INFO: index "onek_unique2" now contains 1000 tuples in 16 pages
102 DETAIL: 3000 index tuples were removed.
103 0 index pages have been deleted, 0 are currently reusable.
104 CPU 0.00s/0.07u sec elapsed 0.23 sec.
105 INFO: index "onek_hundred" now contains 1000 tuples in 13 pages
106 DETAIL: 3000 index tuples were removed.
107 0 index pages have been deleted, 0 are currently reusable.
108 CPU 0.01s/0.08u sec elapsed 0.17 sec.
109 INFO: index "onek_stringu1" now contains 1000 tuples in 48 pages
110 DETAIL: 3000 index tuples were removed.
111 0 index pages have been deleted, 0 are currently reusable.
112 CPU 0.01s/0.09u sec elapsed 0.59 sec.
113 INFO: "onek": removed 3000 tuples in 108 pages
114 DETAIL: CPU 0.01s/0.06u sec elapsed 0.07 sec.
115 INFO: "onek": found 3000 removable, 1000 nonremovable tuples in 143 pages
116 DETAIL: 0 dead tuples cannot be removed yet.
117 There were 0 unused item pointers.
118 0 pages are entirely empty.
119 CPU 0.07s/0.39u sec elapsed 1.56 sec.
120 INFO: analyzing "public.onek"
121 INFO: "onek": 36 pages, 1000 rows sampled, 1000 estimated total rows
122 VACUUM
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126 There is no VACUUM statement in the SQL standard.
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129 vacuumdb [vacuumdb(1)], in the documentation
130SQL - Language Statements 2008-06-08 VACUUM()