Editing Cache replacement policies (section)

==== Low inter-reference recency set (LIRS) ====
{{Further|LIRS caching algorithm}}
LIRS is a page replacement algorithm with better performance than LRU and other, newer replacement algorithms. Reuse distance is a metric for dynamically ranking accessed pages to make a replacement decision.<ref>{{cite journal | last1=Jiang | first1=Song | last2=Zhang | first2=Xiaodong | title=LIRS: An efficient low inter-reference recency set replacement policy to improve buffer cache performance | journal=ACM SIGMETRICS Performance Evaluation Review | publisher=Association for Computing Machinery | volume=30 | issue=1 | pages=31–42 | doi=10.1145/511399.511340 | issn=0163-5999 | date=June 2002 | url=http://web.cse.ohio-state.edu/hpcs/WWW/HTML/publications/papers/TR-02-6.pdf}}</ref> LIRS addresses the limits of LRU by using recency to evaluate inter-reference recency (IRR) to make a replacement decision.

[[File:LIRSalgoworking.png|center|alt=Diagram of the LIRS algorithm]]

In the diagram, X indicates that a block is accessed at a particular time. If block A1 is accessed at time 1, its recency will be 0; this is the first-accessed block and the IRR will be 1, since it predicts that A1 will be accessed again in time 3. In time 2, since A4 is accessed, the recency will become 0 for A4 and 1 for A1; A4 is the most recently accessed object, and the IRR will become 4. At time 10, the LIRS algorithm will have two sets: an LIR set = {A1, A2} and an HIR set = {A3, A4, A5}. At time 10, if there is access to A4 a miss occurs; LIRS will  evict A5 instead of A2 because of its greater recency.