code: public void update(TransactionBase tx, Map<K, V> updates) {
      combineQ.addAll(tx, updates);
    }
docs: Queues updates for a collision free map. These updates will be made by an Observer executing
  another transaction. This method will not collide with other transaction queuing updates for
  the same keys.
  
  @param tx This transaction will be used to make the updates.
  @param updates The keys in the map should correspond to keys in the collision free map being
  updated. The values in the map will be queued for updating.