@Override
  public void start() {
    // Try to get cluster information once, to avoid immediate cluster-update event in WM.
    clusterState.initClusterInfo();
    clusterStateUpdateThread.start();
  }
Implements query resource allocation using guaranteed tasks.
ql/src/java/org/apache/hadoop/hive/ql/exec/tez/GuaranteedTasksAllocator.java