PG function generates a mongodb's objectId

object_id.sql

CREATE SEQUENCE IF NOT EXISTS object_id_counter AS int;

CREATE OR REPLACE FUNCTION generate_object_id() RETURNS CHAR(24)
AS $$
DECLARE
  id CHAR(24);
BEGIN
  SELECT right(to_hex(floor(extract(epoch from now()))::integer), 8)
    || right(lpad(to_hex(pg_backend_pid()), 10, '0'), 10)
    || right(lpad(to_hex(nextval('object_id_counter')), 6, '0'), 6)
  INTO STRICT id;
  RETURN id;
END;
$$ LANGUAGE plpgsql;