(PHP 4 >= 4.3.0, PHP 5)
pg_get_pid — Ping database connection
$connection
      )pg_get_pid() gets backend (database server process) PID. PID is useful to check if NOTIFY message is sent from other process or not.
See also pg_get_notify()
Example #1 PostgreSQL backend PID
<?php 
$conn = pg_pconnect ("dbname=publisher");
if (!$conn) {
    echo "An error occured.\n";
    exit;
}
// Backend process PID. Use PID with pg_get_notify()
$pid = pg_get_pid($conn);
?>