pg_autovacuum

PostgreSQL 8.3.3 Documentation
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# 44.10. `pg_autovacuum`

The catalog `pg_autovacuum` stores optional per-relation configuration parameters for the autovacuum daemon. If there is an entry here for a particular relation, the given parameters will be used for autovacuuming that table. If no entry is present, the system-wide defaults will be used. For more information about the autovacuum daemon, see Section 23.1.4.

> Note: It is likely that `pg_autovacuum` will disappear in a future release, with the information instead being kept in `pg_class`.`reloptions` entries.

Table 44-10. `pg_autovacuum` Columns

Name | Type | References | Description
--- | --- | --- | ---
`vacrelid` | `oid` | ``pg_class`.oid` | The table this entry is for
`enabled` | `bool` |  | If false, this table will not be autovacuumed, except to prevent transaction ID wraparound
`vac_base_thresh` | `integer` |  | Minimum number of modified tuples before vacuum
`vac_scale_factor` | `float4` |  | Multiplier for `reltuples` to add to `vac_base_thresh`
`anl_base_thresh` | `integer` |  | Minimum number of modified tuples before analyze
`anl_scale_factor` | `float4` |  | Multiplier for `reltuples` to add to `anl_base_thresh`
`vac_cost_delay` | `integer` |  | Custom `vacuum_cost_delay` parameter
`vac_cost_limit` | `integer` |  | Custom `vacuum_cost_limit` parameter
`freeze_min_age` | `integer` |  | Custom `vacuum_freeze_min_age` parameter
`freeze_max_age` | `integer` |  | Custom `autovacuum_freeze_max_age` parameter

The autovacuum daemon will initiate a `VACUUM` operation on a particular table when the number of updated or deleted tuples exceeds `vac_base_thresh` plus `vac_scale_factor` times the number of live tuples currently estimated to be in the relation. Similarly, it will initiate an `ANALYZE` operation when the number of inserted, updated or deleted tuples exceeds `anl_base_thresh` plus `anl_scale_factor` times the number of live tuples currently estimated to be in the relation.

Also, the autovacuum daemon will perform a `VACUUM` operation to prevent transaction ID wraparound if the table's `pg_class`.`relfrozenxid` field attains an age of more than `freeze_max_age` transactions, whether the table has been changed or not, even if `pg_autovacuum`.`enabled` is set to `false` for it. The system will launch autovacuum to perform such `VACUUM`s even if autovacuum is otherwise disabled. See Section 23.1.3 for more about wraparound prevention.

Any of the numerical fields can contain `-1` (or indeed any negative value) to indicate that the system-wide default should be used for this particular value. Observe that the `vac_cost_delay` variable inherits its default value from the autovacuum_vacuum_cost_delay configuration parameter, or from vacuum_cost_delay if the former is set to a negative value. The same applies to `vac_cost_limit`. Also, autovacuum will ignore attempts to set a per-table `freeze_max_age` larger than the system-wide setting (it can only be set smaller), and the `freeze_min_age` value will be limited to half the system-wide autovacuum_freeze_max_age setting. Note that while you can set `freeze_max_age` very small, or even zero, this is usually unwise since it will force frequent vacuuming.

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