@Override
        public int compareTo(Key o) {
            int compareCacheId = Long.compare(cacheId, o.cacheId);
            return compareCacheId == 0 ? Long.compare(position, o.position) : compareCacheId;
        }
Ensure the capacity of cache

@param cacheStartPosition if the eviction entries contain the current cache, then ensure capacity will return null.
@param size               size of data
@return the indexes of cache blocks
core/src/main/scala/kafka/log/streamaspect/cache/FileCache.java