@Override
        public HFileBlock nextBlockWithBlockType(BlockType blockType) throws IOException {
          HFileBlock blk = nextBlock();
          if (blk.getBlockType() != blockType) {
            throw new IOException(
              "Expected block of type " + blockType + " but found " + blk.getBlockType());
          }
          return blk;
        }
If reading block cost time in milliseconds more than the threshold, a warning will be logged.
hbase-server/src/main/java/org/apache/hadoop/hbase/io/hfile/HFileBlock.java