Server buffer replacement and object prefetch strategy in client-server object-oriented database systems

Abstract

In this thesis, a server caching strategy and an object prefetch strategy are introduced. In a client-server system, when LRU or its variant buffer replacement strategy is used on both the client and the server, the cache performance on the server side is very poor mainly because of pages duplicated in both systems. This paper introduces a server buffer replacement strategy which uses a replaced page-id than a request page-id, for the primary information for its operations. The importance of the corresponding pages in the server cache is decided according to the replaced page-ids that are delivered from clients to the server, so that locations of the pages are altered. Consequently, if a client uses LRU as its buffer replacement strategy, then the server cache is seen by the client as a long virtual client LRU cache extended to the server. Since the replaced page-id is only sent to the server by piggybacking whenever a new page fetch request is sent, the operation to deliver the replaced page-id is simple and induces a minimal overhead. We show that the proposed strategy reveals good performance characteristics in diverse situations, such as single and multiple clients, as well as with various access patterns. We present a new object prefetch strategy, based on exploiting object structure semantics, the object type and the location that the object resides in the disk. Whenever an application fetches an object from the server side, a few OIDs of the previous access objects are delivered to the server by piggybacking. Then the fetch module in the server classifies the access pattern, and then decides the number of objects to be prefetched. In addition, We discus several issues related to the performance such as cache consistency and clustering strategies. We show that the proposed strategy provides good performance on the real system and the simulation environment.