private void startNewSyncThread(String path) {
    ZKData zkData = new ZKData();
    queues.put(path, zkData);
    Thread updater = new ClientZkUpdater(path, zkData);
    updater.setDaemon(true);
    updater.start();
    watchAndCheckExists(path);
  }
Used to store the newest data which we want to sync to client zk.
<p/>
For meta location, since we may reduce the replica number, so here we add a {@code delete} flag
to tell the updater delete the znode on client zk and quit.
hbase-server/src/main/java/org/apache/hadoop/hbase/master/zksyncer/ClientZKSyncer.java