code: public synchronized long get() throws IOException {
      try {
        lastZNodeStat = zooKeeper.exists(fullyQualifiedZNode, false);
        if (lastZNodeStat == null) {
          return -1;
        }
        byte[] data =
            zooKeeper.getData(fullyQualifiedZNode, false, lastZNodeStat);
        WritableUtil.readWritableFromByteArray(data, maxTxIdWritable);
        return maxTxIdWritable.get();
      } catch (KeeperException e) {
        keeperException("Unrecoverable ZooKeeper error reading " +
            fullyQualifiedZNode, e);
        return -1; // This is never reached
      } catch (InterruptedException e) {
        interruptedException("Interrupted reading " +
            fullyQualifiedZNode, e);
        return -1; // This is never reached
      }
    }
docs: Get the current max transaction id from ZooKeeper
  @return The current max transaction id
  @throws IOException If there is an error talking to ZooKeeper