code: @SuppressWarnings("unchecked")
      private void performRollback(Subscriber<? super T> subscriber, State state) {
          debug("rolling back");
          query.context().endTransactionObserve();
          Conditions.checkTrue(!Util.isAutoCommit(state.con));
          Util.rollback(state.con);
          // must close before onNext so that connection is released and is
          // available to a query that might process the onNext
          close(state);
          subscriber.onNext((T) Integer.valueOf(0));
          debug("rolled back");
          complete(subscriber);
      }
docs: Rolls back the current transaction. Throws {@link RuntimeException} if
  connection is in autoCommit mode.
  
  @param subscriber
  @param state