Editing Cache replacement policies (section)

==== {{anchor|MRU|Most recently used (MRU)}}Most-recently-used (MRU) ====

Unlike LRU, MRU discards the most-recently-used items first. At the 11th [[VLDB conference]], Chou and DeWitt said: "When a file is being repeatedly scanned in a [looping sequential] reference pattern, MRU is the best [[page replacement algorithm|replacement algorithm]]."<ref>Hong-Tai Chou and David J. DeWitt. [http://www.vldb.org/conf/1985/P127.PDF An Evaluation of Buffer Management Strategies for Relational Database Systems.] VLDB, 1985.</ref> Researchers presenting at the 22nd VLDB conference noted that for random access patterns and repeated scans over large [[Data set|datasets]] (also known as cyclic access patterns), MRU cache algorithms have more hits than LRU due to their tendency to retain older data.<ref>Shaul Dar, Michael J. Franklin, Björn Þór Jónsson, Divesh Srivastava, and Michael Tan. [http://www.vldb.org/conf/1996/P330.PDF Semantic Data Caching and Replacement.] VLDB, 1996.</ref> MRU algorithms are most useful in situations where the older an item is, the more likely it is to be accessed. The access sequence for the example is A B C D E C D B:

[[File:Mruexample.png|center|alt=Diagram of an MRU algorithm]]

A B C D are placed in the cache, since there is space available. At the fifth access (E), the block which held D is replaced with E since this block was used most recently. At the next access (to D), C is replaced since it was the block accessed just before D.