I recently demonstrated how you can use Rack Mini Profiler to find and fix slow queries. It’s a valuable tool for well-trafficked pages, but sometimes the slowdown is happening on a page you don't visit often, or in a worker task that isn't visible via Rack Mini Profiler. How can you find and fix those slow queries?
Heroku has a feature called expensive queries that can help you out. It shows historical performance data about the queries running on your database: most time consuming, most frequently invoked, slowest execution time, and slowest I/O.
Recently, I used this feature to identify and address some slow queries for a site I run on Heroku named CodeTriage (the best way to...