Editing Cache replacement policies (section)

=== Simple frequency-based policies ===

==== {{anchor|Least-frequently used (LFU)}}Least frequently used (LFU) ====
{{Further|Least frequently used}}
The LFU algorithm counts how often an item is needed; those used less often are discarded first. This is similar to LRU, except that how many times a block was accessed is stored instead of how recently. While running an access sequence, the block which was used the fewest times will be removed from the cache.

==== Least frequent recently used (LFRU) ====
The least frequent recently used (LFRU)<ref>{{cite journal|author=Bilal, Muhammad|display-authors=etal|title=A Cache Management Scheme for Efficient Content Eviction and Replication in Cache Networks|journal=IEEE Access |volume=5|pages=1692–1701|arxiv=1702.04078|bibcode=2017arXiv170204078B|year=2017|doi=10.1109/ACCESS.2017.2669344|s2cid=14517299}}</ref> algorithm combines the benefits of LFU and LRU. LFRU is suitable for network cache applications such as [[Information-centric networking|ICN]], [[Content delivery network|CDNs]], and distributed networks in general. In LFRU, the cache is divided into two partitions: privileged and unprivileged. The privileged partition is protected and, if content is popular, it is pushed into the privileged partition. In replacing the privileged partition, LFRU evicts content from the unprivileged partition; pushes content from the privileged to the unprivileged partition, and inserts new content into the privileged partition. LRU is used for the privileged partition and an approximated LFU (ALFU) algorithm for the unprivileged partition.

==== LFU with dynamic aging (LFUDA) ====
A variant, LFU with dynamic aging (LFUDA), uses dynamic aging to accommodate shifts in a set of popular objects; it adds a cache-age factor to the reference count when a new object is added to the cache or an existing object is re-referenced. LFUDA increments cache age when evicting blocks by setting it to the evicted object's key value, and the cache age is always less than or equal to the minimum key value in the cache.<ref>{{Cite arXiv |eprint = 1001.4135|last1 = Jayarekha|first1 = P.|title = An Adaptive Dynamic Replacement Approach for a Multicast-based Popularity Aware Prefix Cache Memory System|last2 = Nair|first2 = T|class = cs.MM|year = 2010}}</ref> If an object was frequently accessed in the past and becomes unpopular, it will remain in the cache for a long time (preventing newly- or less-popular objects from replacing it). Dynamic aging reduces the number of such objects, making them eligible for replacement,  and LFUDA reduces [[cache pollution]] caused by LFU when a cache is small.