Web Caching and Replication

Chapter 13. Caching the Uncacheable

The usefulness of proxy caching is limited by their low hit rates. Recall from Chapter 7 that realistic object hit rates are around 40 percent, and byte hit rates are even lower. The main reason hit rates are so low is that a large portion of Web requests—up to 43 percent in some studies [Feldmann et al. 1999]—are for uncacheable content. So proxies have just over half the requests to work with. If we factor out uncacheable content, hit rates would be much higher: assuming the above numbers, the hit rate would be around 40%/(100 – 43)% = 70%.

There are a variety of reasons why a content provider may wish to make some content uncacheable. These reasons include collecting accurate usage data, avoiding stale delivery, ...