Postgresql 中文操作指南
Synopsis
VACUUM [ ( option [, ...] ) ] [ table_and_columns [, ...] ]
VACUUM [ FULL ] [ FREEZE ] [ VERBOSE ] [ ANALYZE ] [ table_and_columns [, ...] ]
where option can be one of:
FULL [ boolean ]
FREEZE [ boolean ]
VERBOSE [ boolean ]
ANALYZE [ boolean ]
DISABLE_PAGE_SKIPPING [ boolean ]
SKIP_LOCKED [ boolean ]
INDEX_CLEANUP { AUTO | ON | OFF }
PROCESS_MAIN [ boolean ]
PROCESS_TOAST [ boolean ]
TRUNCATE [ boolean ]
PARALLEL integer
SKIP_DATABASE_STATS [ boolean ]
ONLY_DATABASE_STATS [ boolean ]
BUFFER_USAGE_LIMIT size
and table_and_columns is:
table_name [ ( column_name [, ...] ) ]Description
VACUUM 回收死元组占用的存储空间。在普通的 PostgreSQL 操作中，被更新删除或废弃的元组并未从其表中物理移除；它们会一直保留，直到 VACUUM 完成。因此，有必要定期执行 VACUUM ，尤其是在频繁更新的表上。
VACUUM reclaims storage occupied by dead tuples. 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. Therefore it’s necessary to do VACUUM periodically, especially on frequently-updated tables.
如果没有 table_and_columns 列表， VACUUM 会处理当前用户有权执行 vacuum 的当前数据库中的每张表和物化视图。使用列表后， VACUUM 只会处理这些表。
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. With a list, VACUUM processes only those table(s).
VACUUM ANALYZE 为每张选中的表执行 VACUUM ，然后执行 ANALYZE 。这是一种很方便的组合形式，用于例行维护脚本。请参阅 ANALYZE 了解有关其处理的更多详情。
VACUUM ANALYZE performs a VACUUM and then an ANALYZE for each selected table. This is a handy combination form for routine maintenance scripts. See ANALYZE for more details about its processing.
纯 VACUUM （没有 FULL ）只是回收空间，并使其可重复可用。这种形式的命令可以与表的正常读写操作并行进行，不会获取独占锁。但是，在大多数情况下，额外空间并不会返回给操作系统；它将被保留在同一表中以供重复利用。它还允许我们利用多个 CPU 来处理索引。此功能称为 parallel vacuum 。要禁用此功能，可以使用 PARALLEL 选项，并将并行工作进程指定为零。 VACUUM FULL 将表的整个内容重写到一个无额外空间的新磁盘文件中，从而可以将未使用的空间返回给操作系统。这种形式的速度要慢得多，且需要在每个表正在处理时在其上获取 ACCESS EXCLUSIVE 锁。
Plain VACUUM (without FULL) simply reclaims space and makes it available for re-use. This form of the command can operate in parallel with normal reading and writing of the table, as an exclusive lock is not obtained. 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. It also allows us to leverage multiple CPUs in order to process indexes. This feature is known as parallel vacuum. To disable this feature, one can use PARALLEL option and specify parallel workers as zero. 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. This form is much slower and requires an ACCESS EXCLUSIVE lock on each table while it is being processed.
当选项列表被括号括住时，可以按任意顺序编写选项。如果没有括号，那么必须按照上述确切顺序指定选项。括号语法在 PostgreSQL 9.0 中添加；不带括号的语法已弃用。
When the option list is surrounded by parentheses, the options can be written in any order. Without parentheses, options must be specified in exactly the order shown above. The parenthesized syntax was added in PostgreSQL 9.0; the unparenthesized syntax is deprecated.
Parameters
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FULL
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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.
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FREEZE
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Selects aggressive “freezing” of tuples. Specifying FREEZE is equivalent to performing VACUUM with the vacuum_freeze_min_age and vacuum_freeze_table_age parameters set to zero. Aggressive freezing is always performed when the table is rewritten, so this option is redundant when FULL is specified.
-
-
VERBOSE
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Prints a detailed vacuum activity report for each table.
-
-
ANALYZE
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Updates statistics used by the planner to determine the most efficient way to execute a query.
-
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DISABLE_PAGE_SKIPPING
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Normally, VACUUM will skip pages based on the visibility map. 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. Furthermore, except when performing an aggressive vacuum, some pages may be skipped in order to avoid waiting for other sessions to finish using them. 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.
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SKIP_LOCKED
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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. Note that even with this option, VACUUM may still block when opening the relation’s indexes. Additionally, VACUUM ANALYZE may still block when acquiring sample rows from partitions, table inheritance children, and some types of foreign tables. Also, while VACUUM ordinarily processes all partitions of specified partitioned tables, this option will cause VACUUM to skip all partitions if there is a conflicting lock on the partitioned table.
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INDEX_CLEANUP
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Normally, VACUUM will skip index vacuuming when there are very few dead tuples in the table. The cost of processing all of the table’s indexes is expected to greatly exceed the benefit of removing dead index tuples when this happens. This option can be used to force VACUUM to process indexes when there are more than zero dead tuples. The default is AUTO, which allows VACUUM to skip index vacuuming when appropriate. If INDEX_CLEANUP is set to ON, VACUUM will conservatively remove all dead tuples from indexes. This may be useful for backwards compatibility with earlier releases of PostgreSQL where this was the standard behavior.
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INDEX_CLEANUP can also be set to OFF to force VACUUM to always skip index vacuuming, even when there are many dead tuples in the table. This may be useful when it is necessary to make VACUUM run as quickly as possible to avoid imminent transaction ID wraparound (see Section 25.1.5). However, the wraparound failsafe mechanism controlled by vacuum_failsafe_age will generally trigger automatically to avoid transaction ID wraparound failure, and should be preferred. If index cleanup is not performed regularly, performance may suffer, because as the table is modified indexes will accumulate dead tuples and the table itself will accumulate dead line pointers that cannot be removed until index cleanup is completed.
-
This option has no effect for tables that have no index and is ignored if the FULL option is used. It also has no effect on the transaction ID wraparound failsafe mechanism. When triggered it will skip index vacuuming, even when INDEX_CLEANUP is set to ON.
-
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PROCESS_MAIN
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Specifies that VACUUM should attempt to process the main relation. This is usually the desired behavior and is the default. Setting this option to false may be useful when it is only necessary to vacuum a relation’s corresponding TOAST table.
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PROCESS_TOAST
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Specifies that VACUUM should attempt to process the corresponding TOAST table for each relation, if one exists. This is usually the desired behavior and is the default. Setting this option to false may be useful when it is only necessary to vacuum the main relation. This option is required when the FULL option is used.
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TRUNCATE
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Specifies that VACUUM should attempt to truncate off any empty pages at the end of the table and allow the disk space for the truncated pages to be returned to the operating system. This is normally the desired behavior and is the default unless the vacuum_truncate option has been set to false for the table to be vacuumed. Setting this option to false may be useful to avoid ACCESS EXCLUSIVE lock on the table that the truncation requires. This option is ignored if the FULL option is used.
-
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PARALLEL
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Perform index vacuum and index cleanup phases of VACUUM in parallel using integer background workers (for the details of each vacuum phase, please refer to Table 28.45). The number of workers used to perform the operation is equal to the number of indexes on the relation that support parallel vacuum which is limited by the number of workers specified with PARALLEL option if any which is further limited by max_parallel_maintenance_workers. An index can participate in parallel vacuum if and only if the size of the index is more than min_parallel_index_scan_size. Please note that it is not guaranteed that the number of parallel workers specified in integer will be used during execution. It is possible for a vacuum to run with fewer workers than specified, or even with no workers at all. Only one worker can be used per index. So parallel workers are launched only when there are at least 2 indexes in the table. Workers for vacuum are launched before the start of each phase and exit at the end of the phase. These behaviors might change in a future release. This option can’t be used with the FULL option.
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SKIP_DATABASE_STATS
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Specifies that VACUUM should skip updating the database-wide statistics about oldest unfrozen XIDs. Normally VACUUM will update these statistics once at the end of the command. However, this can take awhile in a database with a very large number of tables, and it will accomplish nothing unless the table that had contained the oldest unfrozen XID was among those vacuumed. Moreover, if multiple VACUUM commands are issued in parallel, only one of them can update the database-wide statistics at a time. Therefore, if an application intends to issue a series of many VACUUM commands, it can be helpful to set this option in all but the last such command; or set it in all the commands and separately issue VACUUM (ONLY_DATABASE_STATS) afterwards.
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ONLY_DATABASE_STATS
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Specifies that VACUUM should do nothing except update the database-wide statistics about oldest unfrozen XIDs. When this option is specified, the table_and_columns list must be empty, and no other option may be enabled except VERBOSE.
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BUFFER_USAGE_LIMIT
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Specifies the [role="bare"]glossary.html#GLOSSARY-BUFFER-ACCESS-STRATEGYBuffer Access Strategy ring buffer size for VACUUM. This size is used to calculate the number of shared buffers which will be reused as part of this strategy. 0 disables use of a Buffer Access Strategy. If ANALYZE is also specified, the BUFFER_USAGE_LIMIT value is used for both the vacuum and analyze stages. This option can’t be used with the FULL option except if ANALYZE is also specified. When this option is not specified, VACUUM uses the value from vacuum_buffer_usage_limit. Higher settings can allow VACUUM to run more quickly, but having too large a setting may cause too many other useful pages to be evicted from shared buffers. The minimum value is 128 kB and the maximum value is 16 GB.
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boolean
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Specifies whether the selected option should be turned on or off. You can write TRUE, ON, or 1 to enable the option, and FALSE, OFF, or 0 to disable it. The boolean value can also be omitted, in which case TRUE is assumed.
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integer
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Specifies a non-negative integer value passed to the selected option.
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size
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Specifies an amount of memory in kilobytes. Sizes may also be specified as a string containing the numerical size followed by any one of the following memory units: B (bytes), kB (kilobytes), MB (megabytes), GB (gigabytes), or TB (terabytes).
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table_name
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The name (optionally schema-qualified) of a specific table or materialized view to vacuum. If the specified table is a partitioned table, all of its leaf partitions are vacuumed.
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column_name
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The name of a specific column to analyze. Defaults to all columns. If a column list is specified, ANALYZE must also be specified.
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Outputs
当指定 VERBOSE 时， VACUUM 将发出进度消息以指示当前正在处理哪个表。还会打印有关表的各种统计信息。
When VERBOSE is specified, VACUUM emits progress messages to indicate which table is currently being processed. Various statistics about the tables are printed as well.
Notes
通常，要 vacuum 一个表，用户必须是该表的拥有者或超级用户。但是，允许数据库所有者 vacuum 其数据库中的所有表，共享目录除外。（共享目录的限制表示，真正的数据库级 VACUUM 只可由超级用户执行。） VACUUM 将跳过调用用户没有权限真空的任何表。
To vacuum a table, one must ordinarily be the table’s owner or a superuser. However, database owners are allowed to vacuum all tables in their databases, except shared catalogs. (The restriction for shared catalogs means that a true database-wide VACUUM can only be performed by a superuser.) VACUUM will skip over any tables that the calling user does not have permission to vacuum.
VACUUM 无法在事务块内执行。
VACUUM cannot be executed inside a transaction block.
对于具有 GIN 索引的表，任何形式的 VACUUM 也会通过将待决的索引条目移到 GIN 主索引结构的适当位置，来完成所有待决的索引插入。请参阅 Section 70.4.1 了解更多详情。
For tables with GIN indexes, VACUUM (in any form) also completes any pending index insertions, by moving pending index entries to the appropriate places in the main GIN index structure. See Section 70.4.1 for details.
我们建议定期 vacuum 所有数据库以删除死行。PostgreSQL 包括一项“自动 vacuum”功能，可以自动执行例程 vacuum 维护。有关自动 vacuum 和手动 vacuum 的更多信息，请参阅 Section 25.1 。
We recommend that all databases be vacuumed regularly in order to remove dead rows. PostgreSQL includes an “autovacuum” facility which can automate routine vacuum maintenance. For more information about automatic and manual vacuuming, see Section 25.1.
不建议常规使用 FULL 选项，但在特殊情况下可能有用。一个示例是已删除或更新表中的大部分行，并希望表在物理上缩小以占用更少的磁盘空间并允许更快的表扫描。 VACUUM FULL 通常会使表比普通 VACUUM 缩小更多。
The FULL option is not recommended for routine use, but might be useful in special cases. An example is when you have deleted or updated most of the rows in a table and would like the table to physically shrink to occupy less disk space and allow faster table scans. VACUUM FULL will usually shrink the table more than a plain VACUUM would.
PARALLEL 选项仅用于 vacuum 用途。如果将此选项与 ANALYZE 选项一起指定，则它不会影响 ANALYZE 。
The PARALLEL option is used only for vacuum purposes. If this option is specified with the ANALYZE option, it does not affect ANALYZE.
VACUUM 会大幅增加 I/O 流量，这可能会导致其他活动会话的性能不佳。因此，有时建议使用基于成本的真空延迟功能。对于并行 vacuum，每个工作进程都将按该工作进程完成的工作成比例地休眠。请参阅 Section 20.4.4 了解更多详情。
VACUUM causes a substantial increase in I/O traffic, which might cause poor performance for other active sessions. Therefore, it is sometimes advisable to use the cost-based vacuum delay feature. For parallel vacuum, each worker sleeps in proportion to the work done by that worker. See Section 20.4.4 for details.
在没有 FULL 选项的情况下运行 VACUUM 的每个后端都会在 pg_stat_progress_vacuum 视图中报告其进度。在 VACUUM FULL 下运行的后端会改为在 pg_stat_progress_cluster 视图中报告其进度。请参阅 Section 28.4.5 和 Section 28.4.2 了解更多详情。
Each backend running VACUUM without the FULL option will report its progress in the pg_stat_progress_vacuum view. Backends running VACUUM FULL will instead report their progress in the pg_stat_progress_cluster view. See Section 28.4.5 and Section 28.4.2 for details.