@Override
  public void init(AtomicBoolean stop) throws Exception {
    super.init(stop);

    // Get our own instance of the transaction handler
    txnHandler = TxnUtils.getTxnStore(conf);
    metadataCache = new MetadataCache(isCacheEnabled());
    // Initialize the RawStore, with the flag marked as true. Since its stored as a ThreadLocal variable in the
    // HMSHandlerContext, it will use the compactor related pool.
    MetastoreConf.setBoolVar(conf, COMPACTOR_USE_CUSTOM_POOL, true);
    getMSForConf(conf);
  }
Compactor threads that runs in the metastore. It uses a {@link TxnStore}
to access the internal database.
ql/src/java/org/apache/hadoop/hive/ql/txn/compactor/MetaStoreCompactorThread.java