PostgreSQL 9.1beta2 Documentation
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# 18.9. Automatic Vacuuming

These settings control the behavior of the autovacuum feature. Refer to Section 23.1.5 for more information.

`autovacuum` (`boolean`)

  Controls whether the server should run the autovacuum launcher daemon. This is on by default; however, track_counts must also be enabled for autovacuum to work. This parameter can only be set in the `postgresql.conf` file or on the server command line.

  Note that even when this parameter is disabled, the system will launch autovacuum processes if necessary to prevent transaction ID wraparound. See Section 23.1.4 for more information.

`log_autovacuum_min_duration` (`integer`)

  Causes each action executed by autovacuum to be logged if it ran for at least the specified number of milliseconds. Setting this to zero logs all autovacuum actions. Minus-one (the default) disables logging autovacuum actions. For example, if you set this to `250ms` then all automatic vacuums and analyzes that run 250ms or longer will be logged. In addition, when this parameter is set to any value other than `-1`, a message will be logged if an autovacuum action is skipped due to the existence of a conflicting lock. Enabling this parameter can be helpful in tracking autovacuum activity. This setting can only be set in the `postgresql.conf` file or on the server command line.

`autovacuum_max_workers` (`integer`)

  Specifies the maximum number of autovacuum processes (other than the autovacuum launcher) which may be running at any one time. The default is three. This parameter can only be set at server start.

`autovacuum_naptime` (`integer`)

  Specifies the minimum delay between autovacuum runs on any given database. In each round the daemon examines the database and issues `VACUUM` and `ANALYZE` commands as needed for tables in that database. The delay is measured in seconds, and the default is one minute (`1min`). This parameter can only be set in the `postgresql.conf` file or on the server command line.

`autovacuum_vacuum_threshold` (`integer`)

  Specifies the minimum number of updated or deleted tuples needed to trigger a `VACUUM` in any one table. The default is 50 tuples. This parameter can only be set in the `postgresql.conf` file or on the server command line. This setting can be overridden for individual tables by changing storage parameters.

`autovacuum_analyze_threshold` (`integer`)

  Specifies the minimum number of inserted, updated or deleted tuples needed to trigger an `ANALYZE` in any one table. The default is 50 tuples. This parameter can only be set in the `postgresql.conf` file or on the server command line. This setting can be overridden for individual tables by changing storage parameters.

`autovacuum_vacuum_scale_factor` (`floating point`)

  Specifies a fraction of the table size to add to `autovacuum_vacuum_threshold` when deciding whether to trigger a `VACUUM`. The default is 0.2 (20% of table size). This parameter can only be set in the `postgresql.conf` file or on the server command line. This setting can be overridden for individual tables by changing storage parameters.

`autovacuum_analyze_scale_factor` (`floating point`)

  Specifies a fraction of the table size to add to `autovacuum_analyze_threshold` when deciding whether to trigger an `ANALYZE`. The default is 0.1 (10% of table size). This parameter can only be set in the `postgresql.conf` file or on the server command line. This setting can be overridden for individual tables by changing storage parameters.

`autovacuum_freeze_max_age` (`integer`)

  Specifies the maximum age (in transactions) that a table's `pg_class`.`relfrozenxid` field can attain before a `VACUUM` operation is forced to prevent transaction ID wraparound within the table. Note that the system will launch autovacuum processes to prevent wraparound even when autovacuum is otherwise disabled.

  Vacuum also allows removal of old files from the `pg_clog` subdirectory, which is why the default is a relatively low 200 million transactions. This parameter can only be set at server start, but the setting can be reduced for individual tables by changing storage parameters. For more information see Section 23.1.4.

`autovacuum_vacuum_cost_delay` (`integer`)

  Specifies the cost delay value that will be used in automatic `VACUUM` operations. If -1 is specified, the regular vacuum_cost_delay value will be used. The default value is 20 milliseconds. This parameter can only be set in the `postgresql.conf` file or on the server command line. This setting can be overridden for individual tables by changing storage parameters.

`autovacuum_vacuum_cost_limit` (`integer`)

  Specifies the cost limit value that will be used in automatic `VACUUM` operations. If -1 is specified (which is the default), the regular vacuum_cost_limit value will be used. Note that the value is distributed proportionally among the running autovacuum workers, if there is more than one, so that the sum of the limits of each worker never exceeds the limit on this variable. This parameter can only be set in the `postgresql.conf` file or on the server command line. This setting can be overridden for individual tables by changing storage parameters.

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