Effective caching for NetNews servers

Since the traffic of NetNews is increasing, keeping all articles becomes se rious problem from a viewpoint of waste of network bandwidth and the amount of disk usage. In addition, users read not all incoming articles. We have proposed several caching algorithms to overcome this problem and shown that a selective prefetch scheme gives the best system performance among the pr oposed ones. However, since the selective prefetch scheme employed a simple selecting policy, the scheme gave low hit ratio in some cases. Therefore, this paper intends to improve the selective prefetch scheme from a viewpoin t of the amount of disk usage as well as hit ratio. In this paper, we divid e the scheme into three factors: reference span, criterion, and threshold i n criterion. Through simulation experiments using actual NetNews logs, we i nvestigate the influence of the factors of the reference span and the thres hold to system performance. As a result, it is shown that the reference spa n is more significant factor than the threshold, the selective prefetch sch eme with a value around the seven days reference span keeps high hit ratio and reduces the amount of disk usage.