private BlockCacheKey buildCacheBlockKey(long offset, BlockType blockType) {
    if (path != null) {
      return new BlockCacheKey(path, offset, true, blockType);
    }
    return new BlockCacheKey(name, offset, true, blockType);
  }
Caches the last written HFile block.
@param offset the offset of the block we want to cache. Used to determine the cache key.
hbase-server/src/main/java/org/apache/hadoop/hbase/io/hfile/HFileWriterImpl.java