System Administration Functions

• Configuration Settings Functions
• Server Signaling Functions
• Database Object Size Functions

The functions described in this section are used to control and monitor a Tacnode installation.

Configuration Settings Functions

Table 8.67 shows the functions available to query and alter run-time configuration parameters.

Table Configuration Settings Functions

current_setting ( setting_name text [, missing_ok boolean ] ) → text Returns the current value of the setting setting_name. If there is no such setting, current_setting throws an error unless missing_ok is supplied and is true (in which case NULL is returned). This function corresponds to the SQL command SHOW. current_setting('datestyle') → ISO, MDY

set_config ( setting_name text, new_value text, is_local boolean ) → text Sets the parameter setting_name to new_value, and returns that value. If is_local is true, the new value will only apply during the current transaction. If you want the new value to apply for the rest of the current session, use false instead. This function corresponds to the SQL command SET. set_config('log_statement_stats', 'off', false) → off

Server Signaling Functions

The functions shown in Table 8.68 send control signals to other server processes. Use of these functions is restricted to superusers by default but access may be granted to others using GRANT, with noted exceptions.

Each of these functions returns true if the signal was successfully sent and false if sending the signal failed.

Table Server Signaling Functions

pg_cancel_backend ( pid integer ) → boolean Cancels the current query of the session whose backend process has the specified process ID. This is also allowed if the calling role is a member of the role whose backend is being canceled or the calling role has been granted pg_signal_backend, however only superusers can cancel superuser backends.

pg_terminate_backend ( pid integer, timeout bigint DEFAULT 0 ) → boolean Terminates the session whose backend process has the specified process ID. This is also allowed if the calling role is a member of the role whose backend is being terminated or the calling role has been granted pg_signal_backend, however only superusers can terminate superuser backends. If timeout is not specified or zero, this function returns true whether the process actually terminates or not, indicating only that the sending of the signal was successful. If the timeout is specified (in milliseconds) and greater than zero, the function waits until the process is actually terminated or until the given time has passed. If the process is terminated, the function returns true. On timeout, a warning is emitted and false is returned.

pg_cancel_backend and pg_terminate_backend send signals (SIGINT or SIGTERM respectively) to backend processes identified by process ID. The process ID of an active backend can be found from the pid column of the pg_stat_activity view, or by listing the postgres processes on the server (using ps on Unix or the Task Manager on Windows). The role of an active backend can be found from the usename column of the pg_stat_activity view.

Database Object Size Functions

The functions shown in this table calculate the disk space usage of database objects, or assist in presenting or understanding usage results. All these functions return sizes measured in bytes.

Table Database Object Size Functions

pg_database_size ( name ) → bigint pg_database_size ( oid ) → bigint Computes the total disk space used by the database with the specified name or OID. To use this function, you must have CONNECT privilege on the specified database (which is granted by default) or have privileges of the pg_read_all_stats role. pg_database_size('postgres') → 8053063

pg_relation_size ( relation regclass [, fork text ] ) → bigint Computes the disk space used by one “fork” of the specified relation. (Note that for most purposes it is more convenient to use the higher-level function pg_table_size, which sums the sizes of all forks.) With one argument, this returns the size of the main data fork of the relation. The second argument can be provided to specify which fork to examine:

• main returns the size of the main data fork of the relation
• fsm returns the size of the Free Space Map associated with the relation
• vm returns the size of the Visibility Map associated with the relation
• init returns the size of the initialization fork, if any, associated with the relation pg_relation_size('pg_class') → 98304

pg_table_size ( regclass ) → bigint Computes the disk space used by the specified table, excluding indexes (but including its TOAST table if any, free space map, and visibility map). pg_table_size('pg_class') → 122880