The example We had to deal with in the real world was the onslaught of visitors during the American Thanksgiving holiday. The company I worked for would post th

The example We had to deal with in the real world was the onslaught of visitors during the American Thanksgiving holiday. The company I worked for would post the ads for Black Friday and Cyber Monday. Yeah, nothing like getting >500K RPS on a 2 DB server setup (Main & Backup) that was highly tuned that would drop to it's knees. The traffic we got, didn't really turn in to that much overall profit, which meant, we couldn't have a huge cluster of DB's to handle the load. Having a caching system using Memcached (120 second query cache), we were able to handle that load like it was nothing. We used caching on other parts of the system, but the DB cache is what saved us from having to leave the dinner table every 15 minutes.