@Override
    public String toString() {
      StringBuilder sb = new StringBuilder();
      sb.append("size=" + rootCount).append("\n");
      for (int i = 0; i < rootCount; i++) {
        sb.append("key=").append((blockKeys[i])).append("\n  offset=").append(blockOffsets[i])
          .append(", dataSize=" + blockDataSizes[i]).append("\n");
      }
      return sb.toString();
    }
Adds a new entry in the root block index. Only used when reading.
@param key      Last key in the block
@param offset   file offset where the block is stored
@param dataSize the uncompressed data size
hbase-server/src/main/java/org/apache/hadoop/hbase/io/hfile/HFileBlockIndex.java