Cache-Aside and the Null Sentinel Pattern

There is a class of bugs that are worse than crashes. Crashes are loud, they page someone and they get fixed. This one is quiet. Your cache is running, your hit rate looks fine. But your database is being hit on every single request for data that has not changed at all. I hit this while implementing cache-aside in a side project. A Quick Recap of How Cache-Aside Works Before getting into the bug, let me explain the pattern I was using. Cache-aside is the most common caching strategy: A request c