Isn't the secret to fast, scalable websites to cache everything? Caching, if not the secret sauce of many a website, is it at least a popular condiment. But not so fast says Peter Zaitsev in Beyond great cache hit ratio. The point Peter makes is that we read about websites like Amazon and Facebook that can literally make hundreds of calls to satisfy a user request. Even if you have an awesome cache hit ratio, pages can still be slow because making and processing all those requests takes time. The solution is to remove requests all together. You do this by caching larger blocks so you have to make fewer requests.
The post has a lot of good advice worth reading: 1) Make non cacheable blocks as small as possible, 2) Maximize amount of uses of the cache item, 3) Control invalidation, 4) Multi-Get.