This post on www.ilovebonnie.net documents some impressive system performance improvements by the addition of Squid Cache (a caching proxy) and APC Cache (opcode cache for PHP).
* Apache is able to deliver roughly 700% more requests per second with Squid when serving 1KB and 100KB images.
* Server load is reduced using Squid because the server does not have to create a bunch of Apache processes to handle the requests.
* APC Cache took a system that could barely handle 10-20 requests per second to handling 50-60 requests per second. A 400% increase.
* APC allowed the load times to remain under 5 seconds even with 200 concurrent threads slamming on the server.
* These two caches are easy to setup and install and allow you to get a lot more performance out of them.
The post has an in-depth discussion and a number of supporting charts. The primary point is how simple it can be to improve performance and scalability by adding caching.
