public void stop() {
    if (mainExecutor != null) {
      mainExecutor.shutdown();
      mainExecutor = null;
    }
  }
TezSessionPoolManagerMetrics collects, aggregates and exposes data from Tez sessions to Hive's own MetricsFactory.
This is independent of the Tez DagClient which is active only while running DAGs.
ql/src/java/org/apache/hadoop/hive/ql/exec/tez/TezSessionPoolManagerMetrics.java