Probability based replacement algorithm for WWW server arrays

This paper describes a scalable Web server array architecture which uses a caching policy called the probability based replacement (PBR) algorithm. The server array consists of a central server and several Web servers. The central server stores the whole document set, and sends the user requested documents to the Web servers by a technique called the selective broadcast technique. Web documents are cached in the Web servers and are replaced based on the PBR algorithm. Performance comparison using NASA and ClarkNet access logs between PBR server arrays and purely mirrored Web servers is performed. The results show that with 10% document caching, the maximum throughput of the former one is nearly the same as that of mirrored Web servers. The PBR server arrays, however, require much smaller disk storage in the Web servers than the mirrored Web servers. The PBR server arrays are also much more scalable than the mirrored ones.