code: public void updateLimit(StorageTransaction tx, String counterId, long limit) throws IOException {
      tx.updateLimitForCounter(counterId, limit);
    }
docs: Must be called within a TransactionCallable. (?)
  
  <p>Augments the transaction with operations to persist the given limit in Datastore. So long as
  there has been no preceding successful updateLimit operation, no limit is applied in
  updateCounter operations on this counter.