Update ddl.sql

client_pid(worker_pid)

The server running pg_timetable may be different, but coincidentally the pid may be the same.

Duplicate execution can be prevented by adding the client_addr column as shown below.

---------  -------------------------------------------------------------------
SQL> select * from timetable.active_sessions
client_id 
---------  -------------------------------------------------------------------
14	pg_timetable	28417	167.71.214.34	2022-08-07 14:12:24.333 +0900
14	pg_timetable	28418	167.71.214.34	2022-08-07 14:12:24.366 +0900
14	pg_timetable	28422	128.199.132.200	2022-08-07 14:12:29.563 +0900
14	pg_timetable	28423	128.199.132.200	2022-08-07 14:12:29.589 +0900

internal/pgengine/sql/ddl.sql

@@ -109,6 +109,7 @@ CREATE UNLOGGED TABLE timetable.active_session(
     client_pid  BIGINT  NOT NULL,
     client_name TEXT    NOT NULL,
     server_pid  BIGINT  NOT NULL,
+    client_addr INET  NOT NULL,
     started_at  TIMESTAMPTZ DEFAULT now()
 );
 
@@ -187,15 +188,15 @@ BEGIN
     PERFORM 1
         FROM timetable.active_session s
         WHERE
-            s.client_pid <> worker_pid
+            s.client_addr <> inet_client_addr()
             AND s.client_name = worker_name
         LIMIT 1;
     IF FOUND THEN
         RAISE NOTICE 'Another client is already connected to server with name: %', worker_name;
         RETURN FALSE;
     END IF;
     -- insert current session information
-    INSERT INTO timetable.active_session(client_pid, client_name, server_pid) VALUES (worker_pid, worker_name, pg_backend_pid());
+    INSERT INTO timetable.active_session(client_pid, client_name, server_pid, client_addr) VALUES (worker_pid, worker_name, pg_backend_pid(), inet_client_addr());
     RETURN TRUE;
 END;
 $CODE$