Web Caching

Why Not Join a Hierarchy?

Now that you know about the advantages of hierarchical caching, it is also important to consider carefully some of the disadvantages and potential problems. Any improvements in performance may be offset by one or more of the following issues.

Some of these issues are significant only when you establish a relationship with caches outside your own organization. For example, you probably trust a neighbor cache within your company more than you trust one that belongs to another company. The presence or absence of a business agreement between two organizations also affects many of these issues. For instance, when you pay another party for a service, it is much easier to get problems resolved quickly.

Trust

You may recall that we talked about trust in Chapter 3. That discussion focused on content integrity and privacy concerns with logfile information. These issues are even more important when you join a cache hierarchy. Not only must you trust your immediate neighbors, but you must also trust all of their neighbors, and so on. Again, you are trusting them to protect the privacy of your web requests and to deliver correct, unmodified documents. Hierarchies can be quite large. It’s possible that your requests and responses pass through five or more caching proxies between you and the origin server.

When you get a web page, how can you tell if it is authentic? Currently, there is no good way. Such a scheme would most likely involve digital signatures and public ...