public String getFailedCause() {
    return stateMachine.getFailureCauses().stream()
        .findFirst()
        .map(Throwable::getMessage)
        .orElse("");
  }
return Message string of all failures
iotdb-core/datanode/src/main/java/org/apache/iotdb/db/queryengine/execution/fragment/FragmentInstanceContext.java