PostgreSQL 8.2.20 Documentation
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# 17.9. Automatic Vacuuming

These settings control the behavior of the autovacuum feature. Refer to Section 22.1.4 for more information.

`autovacuum` (`boolean`)

  Controls whether the server should run the autovacuum daemon. This is off by default. `stats_start_collector` and `stats_row_level` must also be turned on for autovacuum to work. This parameter can only be set in the `postgresql.conf` file or on the server command line.

`autovacuum_naptime` (`integer`)

  Specifies the delay between activity rounds for the autovacuum daemon. In each round the daemon examines one 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 (`1m`). 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 periodically launch autovacuum processes in order to prevent transaction ID wraparound. See Section 22.1.3 for more information.

`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 500 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 entries in `pg_autovacuum`.

`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 250 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 entries in `pg_autovacuum`.

`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 entries in `pg_autovacuum`.

`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 entries in `pg_autovacuum`.

`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. The default is 200 million transactions. This parameter can only be set at server start, but the setting can be reduced for individual tables by entries in `pg_autovacuum`. For more information see Section 22.1.3.

`autovacuum_vacuum_cost_delay` (`integer`)

  Specifies the cost delay value that will be used in automatic `VACUUM` operations. If `-1` is specified (which is the default), the regular vacuum_cost_delay value will be used. 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 entries in `pg_autovacuum`.

`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. 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 entries in `pg_autovacuum`.

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