Theoretical Evidence for the Superiority of LRU-2 over LRU for the Paging Problem

The paging algorithm LRU-2 was proposed for use in database disk buffering and shown experimentally to perform better than LRU [O’Neil, O’Neil, and Weikum, 1993]. We compare LRU-2 and LRU theoretically, using both the standard competitive analysis and the newer relative worst order analysis. The competitive ratio for LRU-2 is shown to be 2k for cache size k, which is worse than LRU’s competitive ratio of k. However, using relative worst order analysis, we show that LRU2 and LRU are asymptotically comparable in LRU-2’s favor, giving a theoretical justification for the experimental results.