@Override
    void freeBucketEntry(BucketEntry bucketEntry) {
      freeBucketEntryCounter.incrementAndGet();
      super.freeBucketEntry(bucketEntry);
      this.overwiteByteBuff = getOverwriteByteBuff(bucketEntry);
      try {
        this.ioEngine.write(this.overwiteByteBuff, bucketEntry.offset());
      } catch (IOException e) {
        throw new RuntimeException(e);
      }
    }
Overwrite 0xff to the {@link BucketEntry} content to simulate it would be overwrite after the
{@link BucketEntry} is freed.
hbase-server/src/test/java/org/apache/hadoop/hbase/io/hfile/bucket/TestBucketCacheRefCnt.java