Caching only works because human behavior is not random. When parts of your web app are visited, it is more likely they get revisited soon. For example, a user who logged in today is more likely to come back tomorrow than some other user who hasn’t logged in for a few months.
You have been using Memcached for some time, your web app works well, and your hit rate is decent. Recently, your traffic has grown, or maybe your app’s complexity has increased, so you decided to cache more, e.g., user sessions or page fragments, to make your app even speedier.
Monitoring a Memcached instance is essential in determining its effectiveness. Looking at the right metrics can help answer important questions. Is your caching strategy working as expected? Are there bugs that need to be addressed?
Amazon CloudWatch offers a ton of metrics out of the box. A key metric to determine caching performance is missing however; hit rate.