CREATE OR REPLACE
FUNCTION analytics.set_global_visitor(
  aapp_id            INTEGER,
  avisitor_id        INTEGER,
  aglobal_visitor_id text
) RETURNS text AS $$
BEGIN

  aglobal_visitor_id := COALESCE(aglobal_visitor_id, generate_password(64));

  BEGIN

    INSERT INTO analytics.global_visitor (visitor_id, global_visitor_id)
    VALUES (avisitor_id, aglobal_visitor_id);

  exception WHEN unique_violation THEN

    SELECT gv.global_visitor_id
      INTO aglobal_visitor_id
      FROM analytics.global_visitor gv
     WHERE gv.visitor_id = avisitor_id;
  END;

  RETURN aglobal_visitor_id;
END;
$$ LANGUAGE plpgsql security definer;