@Override
        public void freeBlocks() {
          if (freed) {
            return;
          }
          blockTracker.forEach(HFileBlock::release);
          blockTracker = null;
          freed = true;
        }
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