Scope and Accuracy of Analytic and Approximate Results for FIFO, Clock-Based and LRU Caching Performance

Abstract

We evaluate analysis results and approximations for the performance of basic caching methods, assuming independent requests. Compared with simulative evaluations, the analysis results are accurate, but their computation is tractable only within a limited scope. We compare the scalability of analytical FIFO and LRU solutions including extensions for multisegment caches and for caches with data of varying sizes. On the other hand, approximations have been proposed for the FIFO and LRU hit ratio. They are simple and scalable, but their accuracy is confirmed mainly through asymptotic behaviour only for large caches. We derive bounds on the approximation errors in a detailed worst-case study with a focus on small caches. The approximations are extended to data of different sizes. Then a fraction of unused cache space can add to the deviations, which is estimated in order to improve the solution.