@Override
  public void init(AtomicBoolean stop) throws Exception {
    super.init(stop);
    checkInterval = conf.getTimeVar(HiveConf.ConfVars.HIVE_COMPACTOR_CHECK_INTERVAL, TimeUnit.MILLISECONDS);
    compactionExecutor = CompactorUtil.createExecutorWithThreadFactory(
            conf.getIntVar(HiveConf.ConfVars.HIVE_COMPACTOR_REQUEST_QUEUE),
            COMPACTOR_INTIATOR_THREAD_NAME_FORMAT);
    metricsEnabled = MetastoreConf.getBoolVar(conf, MetastoreConf.ConfVars.METRICS_ENABLED) &&
        MetastoreConf.getBoolVar(conf, MetastoreConf.ConfVars.METASTORE_ACIDMETRICS_EXT_ON);
  }
A class to initiate compactions.  This will run in a separate thread.
It's critical that there exactly 1 of these in a given warehouse.
ql/src/java/org/apache/hadoop/hive/ql/txn/compactor/Initiator.java