Sometimes you need to do some profiling of your application to see where performance issues lie. I haven’t done an extensive survey of the options, but a friend recommended rack mini profiler. As the name suggests, this can be used with any rack based framework (so rails, hanami, etc).
There are a number of reasons to use this profiler. Learning to use a profiler, any profiler and how to performance tune is a key part of being a software developer, as opposed to programmer.
It can run in production. You can limit who can access the profiler, and it usually sits in the upper left hand corner with a “page load time”, but you can jump into more detail as needed.
It runs all the time. This lets you have an ambient view of the application (at least the parts that you are touching regularly).
When you are investigating a performance issue, you can easily dive into the views, controllers and SQL queries that your application is making.
It is simple to install, just a simple gem in your Gemfile.
Well worth getting to know, if you are supporting a rails application.