Competitive Paging Algorithms
  The paging problem is that of deciding which pages to keep in a memory of k pages in order to minimize the number of page faults. This paper introduces the marking algorithm, a simple randomized on-line algorithm for the paging problem, and gives a proof that its performance guarantee (competitive ratio) is O(log k). In contrast, no deterministic on-line algorithm can have a performance guarantee better than k. 
Amos Fiat, Richard Karp, Mike Luby, Lyle McGeoch, Daniel Sleator, Neal   E. Young