PDL Abstract

FIFO can be Better than LRU: the Power of Lazy Promotion and Quick Demotion

HotOS ’23, June 22–24, 2023, Providence, RI, USA.

Juncheng Yang, Ziyue Qiu, Yazhuo Zhang*, Yao Yue^, K. V. Rashmi

Carnegie Mellon University
*Emory University
^Pelikan Foundation

LRU has been the basis of cache eviction algorithms for decades, with a plethora of innovations on improving LRU’s miss ratio and throughput. While it is well-known that FIFObased eviction algorithms provide significantly better throughput and scalability, they lag behind LRU on miss ratio, thus, cache efficiency.

We performed a large-scale simulation study using 5307 block and web cache workloads collected in the past two decades.We find that contrary to what common wisdom suggests, some FIFO-based algorithms, such as FIFO-Reinsertion (or CLOCK), are, in fact, more efficient (have a lower miss ratio) than LRU. Moreover, we find that qick demotion — evicting most new objects very quickly — is critical for cache efficiency. We show that when enhanced by qick demotion, not only can state-of-the-art algorithms be more efficient, a simple FIFO-based algorithm can outperform five complex state-of-the-art in terms of miss ratio.