TDC: Pool-Level Object Cache Replacement Algorithm Based on Temperature Density

For mixed HDD and SSD storage scenarios, Ceph Cache Tier provides a tiered caching feature that separates fast and slow storage pools to manage data objects more efficiently. However, due to the limited total capacity of the cache pool, only some data objects can be stored. Performance can be significantly improved when clients focus on accessing hot objects in the cache pool. If a client accesses the cache pool without hitting data, redundant IO operations occur, which increases client access latency and reduces throughput. To improve the hit rate of the Ceph Cache Tier cache pool, this paper proposes a temperature density-based cache replacement algorithm (TDC). The algorithm improves the hit rate of the cache pool by calculating the temperature density of the space consumed by each object and evicting objects with the lowest temperature density, thus evicting objects that contribute less to the hit rate. The algorithm mainly includes object temperature calculation, temperature density calculation and cache replacement policy. Subsequently, we evaluate the TDC algorithm on a real traces dataset using playback workload IO and demonstrate the efficiency of the algorithm in improving the cache hit rate. Finally, we applied the TDC algorithm to a Ceph distributed storage system and verified the performance of the Cache Tier based on the TDC algorithm.