private void logDetailsOfUndoneTasks(long taskInProgress) {
    if (taskInProgress <= thresholdToLogUndoneTaskDetails) {
      ArrayList<ServerName> servers = new ArrayList<>();
      for (Map.Entry<ServerName, AtomicInteger> entry : taskCounterPerServer.entrySet()) {
        if (entry.getValue().get() > 0) {
          servers.add(entry.getKey());
        }
      }
      LOG.info("Left over " + taskInProgress + " task(s) are processed on server(s): " + servers);
    }

    if (taskInProgress <= thresholdToLogRegionDetails) {
      ArrayList<String> regions = new ArrayList<>();
      for (Map.Entry<byte[], AtomicInteger> entry : taskCounterPerRegion.entrySet()) {
        if (entry.getValue().get() > 0) {
          regions.add(Bytes.toString(entry.getKey()));
        }
      }
      LOG.info("Regions against which left over task(s) are processed: " + regions);
    }
  }
The number of task simultaneously executed on a single region server.
hbase-client/src/main/java/org/apache/hadoop/hbase/client/SimpleRequestController.java