Evaluating caching schemes for the X.500 directory

Abstract

The OSI (Open Systems Interconnection) X.500 directory system and other distributed naming systems use name caching to minimize the cost of name lookups for nonlocal names. The authors evaluate the impact of name caching on the performance of the OSI directory system. They consider the issues of cache sizing and cache replacement policies. It was found that a locality of reference property holds in name resolution requests, and hence name caching does increase performance significantly. Using trace-driven simulation, it is shown that small caches (smaller than 30 items) yield hit ratios up to 60% and decrease the average name resolution time by 60%. For small caches, the LRU (least recently used) replacement policy is better than other implementable policies. Large caches yield predictably larger hit ratios. For large caches, however, the LRU policy is not better than a random replacement policy. It was also found that partitioning the cache buffer into a small number of independent caches, each one associated with a different kind of name request, further decreases the average name resolution time.<>