@VisibleForTesting
  public long getTotalTaskEverExecuted() {
    assert (execService != null);
    ThreadPoolExecutor executor = (ThreadPoolExecutor) execService;
    return executor.getTaskCount();
  }
Only for testing purpose. It returns how many number of tasks were executed
in parallel manner at an instant by ExportService.
@return Returns total number of executed tasks in parallel at an instant by ExportService.
ql/src/java/org/apache/hadoop/hive/ql/parse/repl/dump/ExportService.java