@Override
  public Checker newChecker() {
    List<RowChecker> checkers = new ArrayList<>(4);
    checkers.add(new TaskCountChecker(maxTotalConcurrentTasks, maxConcurrentTasksPerServer,
      maxConcurrentTasksPerRegion, tasksInProgress, taskCounterPerServer, taskCounterPerRegion));
    checkers.add(new RequestHeapSizeChecker(maxHeapSizePerRequest));
    checkers.add(new SubmittedSizeChecker(maxHeapSizeSubmit));
    checkers.add(new RequestRowsChecker(maxRowsPerRequest));
    return newChecker(checkers);
  }
The number of task simultaneously executed on a single region server.
hbase-client/src/main/java/org/apache/hadoop/hbase/client/SimpleRequestController.java