private void upsertQueue(String node, byte[] data) {
    ZKData zkData = queues.get(node);
    if (zkData != null) {
      zkData.set(data);
    }
  }
Update the value of the single element in queue if any, or else insert.
<p/>
We only need to synchronize the latest znode value to client ZK rather than synchronize each
time
@param data the data to write to queue
hbase-server/src/main/java/org/apache/hadoop/hbase/master/zksyncer/ClientZKSyncer.java