@Override
  public ValidTxnList getValidTxns(List<TxnType> excludeTxnTypes) throws LockException {
    assert isTxnOpen();
    init();
    try {
      return getMS().getValidTxns(txnId, excludeTxnTypes);
    } catch (TException e) {
      throw new LockException(ErrorMsg.METASTORE_COMMUNICATION_FAILED.getMsg(), e);
    }
  }
Start the heartbeater threadpool and return the task.
@param initialDelay time to delay before first execution, in milliseconds
@return heartbeater
ql/src/java/org/apache/hadoop/hive/ql/lockmgr/DbTxnManager.java