A Distributed List Update Problem

The list update problem is studied in a distributed environment where the set of items is partitioned across two processors and in which the cost of accessing an item is a combination of a list searching cost and a communication cost. A natural generalization of the Move-To-Front (MTF) algorithm, called Distributed Move-To-Front (DMTF), is analyzed under two models of information available to the algorithm. In the global knowledge model (DLUUGK]), the algorithm knows the partition of items in advance, while in the local knowledge model (DLUULK]), this information is unknown to the algorithm. Both competitive and expected value analyses are given. It is shown that for an n-item set, the performance of DMTF is a factor of O(n) worse in the local knowledge model than in the global knowledge model.