Server signaling functions send control signals to other server processes. Only system administrators can use these functions.

pg_cancel_backend(pid int)
Description: Cancels the current query of a backend.

Return type: boolean

Note: pg_cancel_backend sends a query cancellation (SIGINT) signal to the backend process identified by pid. The PID of an active backend process can be found in the pid column of the pg_stat_activity view, or can be found by listing the database process using ps on the server.
pg_reload_conf()
Description: Causes all server processes to reload their configuration files.

Return type: boolean

Note: pg_reload_conf sends a SIGHUP signal to the server. As a result, all server processes reload their configuration files.
pg_rotate_logfile()
Description: Rotates the log files of the server.

Return type: boolean

Note: pg_rotate_logfile instructs the log file manager to immediately switch to a new output file. This function is valid only if the built-in log collector is running.

pg_terminate_backend(pid int)

Description: Terminates a backend thread.

Return type: boolean

Note: Each of these functions returns true if they are successful and false otherwise.

For example:

SELECT pid from pg_stat_activity;
       pid       
-----------------
 140657876268816
 140433774061312
 140433587902208
 140433656592128
 140433723717376
 140433637189376
 140433552770816
 140433481983744
 140433349310208
(1 rows)

SELECT pg_terminate_backend(140657876268816);
 pg_terminate_backend 
----------------------
 t
(1 row)

Server Signaling Functions