PostgreSQL 8.0.0rc2 Documentation
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# 9.20. System Administration Functions

Table 9-44 shows the functions available to query and alter run-time configuration parameters.

Table 9-44. Configuration Settings Functions

Name | Return Type | Description
--- | --- | ---
``current_setting`(`setting_name`)` | `text` | current value of setting
``set_config(`setting_name`, `new_value`, `is_local`)`` | `text` | set parameter and return new value

The function `current_setting` yields the current value of the setting `setting_name`. It corresponds to the SQL command `SHOW`. An example:

    SELECT current_setting('datestyle');

     current_setting
    -----------------
     ISO, MDY
    (1 row)

`set_config` sets the parameter `setting_name` to `new_value`. If `is_local` is `true`, the new value will only apply to the current transaction. If you want the new value to apply for the current session, use `false` instead. The function corresponds to the SQL command `SET`. An example:

    SELECT set_config('log_statement_stats', 'off', false);

     set_config
    ------------
     off
    (1 row)

The function shown in Table 9-45 sends control signals to other server processes. Use of this function is restricted to superusers.

Table 9-45. Backend Signalling Functions

Name | Return Type | Description
--- | --- | ---
``pg_cancel_backend`(`pid`)` | `int` | Cancel a backend's current query

This function returns 1 if successful, 0 if not successful. The process ID (`pid`) of an active backend can be found from the `procpid` column in the `pg_stat_activity` view, or by listing the `postgres` processes on the server with ps.

The functions shown in Table 9-46 assist in making on-line backups. Use of these functions is restricted to superusers.

Table 9-46. Backup Control Functions

Name | Return Type | Description
--- | --- | ---
``pg_start_backup`(`label_text`)` | `text` | Set up for performing on-line backup
``pg_stop_backup`()` | `text` | Finish performing on-line backup

`pg_start_backup` accepts a single parameter which is an arbitrary user-defined label for the backup. (Typically this would be the name under which the backup dump file will be stored.) The function writes a backup label file into the database cluster's data directory, and then returns the backup's starting WAL offset as text. (The user need not pay any attention to this result value, but it is provided in case it is of use.)

`pg_stop_backup` removes the label file created by `pg_start_backup`, and instead creates a backup history file in the WAL archive area. The history file includes the label given to `pg_start_backup`, the starting and ending WAL offsets for the backup, and the starting and ending times of the backup. The return value is the backup's ending WAL offset (which again may be of little interest).

For details about proper usage of these functions, see Section 22.3.

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