Fig. 3

Effect of cache capacity on hit ratio. The figure shows the comparison for the cache hit ratios of different policies when request rate is 500 times/min and the cache capacity C is 64 GB and 32 GB respectively. It can be seen that LRU, LFU, FIFO, and TQC policies all have the same hit ratios when the cache is not full. When t_full = 4.5 h, C = 64 GB, t_full = 2.5 h, C = 32 GB, and the cache is full, different replacement policies start replacing the contents. a and b, consequently, the hit ratios of LRU, TQC, and LFU begin to increase and that of FIFO gradually decreases. In general, the performance of TQC is better than the other three policies. When there is hotspot data, the efficiency of LRU is very good. But sporadic and periodic batch operations will lead to a sharp drop of LRU hit ratio and a serious pollution of the cache. FIFO does not take into account the characteristics of data popularity, so its hit ratio reaches peak of 25% and 12.5% at t_full, then begins to decline and fluctuates around 22.5% and 12.5%. Although the hit ratios of the two are not very different, compared with TQC, LFU records all the access counts of files and as the cache capacity increases, LFU needs to cost more. Therefore, TQC saves more time than LFU and the hit ratio of TQC is also about 12% higher than that of traditional methods