public MemoryUsage getTenuredGenMemoryUsage() {
    if (tenuredGenPool == null) {
      return null;
    }
    return tenuredGenPool.getUsage();
  }
Class that monitors memory usage and notifies the listeners when a certain of threshold of memory is used
after GC (collection usage).
common/src/java/org/apache/hadoop/hive/common/HeapMemoryMonitor.java