Note that even with this option, VACUUM may still block when opening the relation's indexes. Specifies that VACUUM should not wait for any conflicting locks to be released when beginning work on a relation: if a relation cannot be locked immediately without waiting, the relation is skipped. This option disables all page-skipping behavior, and is intended to be used only when the contents of the visibility map are suspect, which should happen only if there is a hardware or software issue causing database corruption. Furthermore, except when performing an aggressive vacuum, some pages may be skipped in order to avoid waiting for other sessions to finish using them. Pages where all tuples are known to be frozen can always be skipped, and those where all tuples are known to be visible to all transactions may be skipped except when performing an aggressive vacuum. Normally, VACUUM will skip pages based on the visibility map. Updates statistics used by the planner to determine the most efficient way to execute a query. Prints a detailed vacuum activity report for each table. Aggressive freezing is always performed when the table is rewritten, so this option is redundant when FULL is specified. Specifying FREEZE is equivalent to performing VACUUM with the vacuum_freeze_min_age and vacuum_freeze_table_age parameters set to zero. Selects aggressive “ freezing” of tuples. Usually this should only be used when a significant amount of space needs to be reclaimed from within 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. Selects “ full” vacuum, which can reclaim more space, but takes much longer and exclusively locks the table. The parenthesized syntax was added in PostgreSQL 9.0 the unparenthesized syntax is deprecated. Without parentheses, options must be specified in exactly the order shown above. When the option list is surrounded by parentheses, the options can be written in any order. This form is much slower and requires an ACCESS EXCLUSIVE lock on each table while it is being processed. VACUUM FULL rewrites the entire contents of the table into a new disk file with no extra space, allowing unused space to be returned to the operating system. To disable this feature, one can use PARALLEL option and specify parallel workers as zero. This feature is known as parallel vacuum. It also allows us to leverage multiple CPUs in order to process indexes. However, extra space is not returned to the operating system (in most cases) it's just kept available for re-use within the same table. This form of the command can operate in parallel with normal reading and writing of the table, as an exclusive lock is not obtained. Plain VACUUM (without FULL) simply reclaims space and makes it available for re-use. See ANALYZE for more details about its processing. This is a handy combination form for routine maintenance scripts. VACUUM ANALYZE performs a VACUUM and then an ANALYZE for each selected table. With a list, VACUUM processes only those table(s). Without a table_and_columns list, VACUUM processes every table and materialized view in the current database that the current user has permission to vacuum. Therefore it's necessary to do VACUUM periodically, especially on frequently-updated tables. In normal PostgreSQL operation, tuples that are deleted or obsoleted by an update are not physically removed from their table they remain present until a VACUUM is done. VACUUM reclaims storage occupied by dead tuples.
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