Least frequently used

LFU is sometimes combined with a Least Recently Used algorithm and called LRFU. The simplest method to employ an LFU algorithm is to assign a counter to every block that is loaded into the cache. Each time a reference is made to that block the counter is increased by one. When the cache reaches capacity and has a new block waiting to be inserted the system will search for the block with the lowest counter and remove it from the cache. While the LFU method may seem like an intuitive approach to memory management it is not without faults. Consider an item in memory which is referenced repeatedly for a short period of time and is not accessed again for an extended period of time. Due to how rapidly it was just accessed its counter has increased drastically even though it will not be used again for a decent amount of time. This leaves other blocks which may actually be used more frequently susceptible to purging simply because they were accessed through a different method. Moreover, new items that just entered the cache are subject to being removed very soon again, because they start with a low counter, even though they might be used very frequently after that. Due to major issues like these, an explicit LFU system is fairly uncommon; instead, there are hybrids that utilize LFU concepts.