postgres=# do $do$
begin
    perform dblink_connect('conn1', 'dbname='||current_database());
    perform dblink_connect('conn2', 'dbname='||current_database());

    perform dblink_send_query('conn1', $$do 'begin perform pg_sleep(10); end;'$$);
    perform dblink_send_query('conn2', $$do 'begin perform pg_sleep(10); end;'$$);
    raise notice '%. Запросы отправлены', clock_timestamp()::text;

    loop
        perform pg_sleep(1);
        exit when (select dblink_is_busy('conn1')) = 0 
              and (select dblink_is_busy('conn2')) = 0;
    end loop;
    raise notice '%. Запросы завершены', clock_timestamp();

    perform dblink_disconnect('conn1');
    perform dblink_disconnect('conn2');
end;
$do$;
NOTICE:  2019-02-21 12:52:18.487223+03. Запросы отправлены
NOTICE:  2019-02-21 12:52:28.499136+03. Запросы завершены
DO