private static int checkAndGet(Configuration conf, String key, int defaultValue) {
    int value = conf.getInt(key, defaultValue);
    if (value <= 0) {
      throw new IllegalArgumentException(key + "=" + value);
    }
    return value;
  }
The number of task simultaneously executed on a single region server.
hbase-client/src/main/java/org/apache/hadoop/hbase/client/SimpleRequestController.java