@Override
  public ConcurrentNavigableMap<K, V> tailMap(K fromKey, boolean inclusive) {
    ArrayHolder<K, V> current = this.holder;
    int index = current.find(fromKey);

    if (!inclusive && index >= 0) {
      index++;
    } else if (index < 0) {
      index = -(index + 1);
    }
    return new CopyOnWriteArrayMap<>(this.keyComparator, new ArrayHolder<>(current.entries, index,
      current.endIndex, current.keyComparator, current.comparator));
  }
A Map that keeps a sorted array in order to provide the concurrent map interface. Keeping a
sorted array means that it's much more cache line friendly, making reads faster than the tree
version. In order to make concurrent reads and writes safe this does a copy on write. There can
only be one concurrent write at a time.
hbase-common/src/main/java/org/apache/hadoop/hbase/types/CopyOnWriteArrayMap.java