Cache Accuracy

  The News Cache gets requests for newsgroups and articles from its clients. If the requested data are already stored in the cache, the News Cache can respond to the request directly. Otherwise the news cache requests these data from its news server, stores them, and sends a copy to the requesting client. Hence successive references to the same data can be answered by the cache without consulting the news server.

Control messages are required to ensure that the cached data are accurate. However, it is not necessary to issue control messages after each client's request, because it is acceptable to provide new articles with a small delay and because News is not a highly dynamic medium. Hence, the control messages may be omitted for newsgroups whose contents have been verified a certain time period (e.g., a few minutes) ago.