I also started to use [New Relic](http://newrelic.com/) to monitor app performance. It's another amazing tool that we recommend. If you don't know New Relic yet, it's a monitoring service which will watch your application health and availability and provide information about the root cause of app performance issues. In my case I was able to see which exactly were the queries that were taking so long to respond. They have these awesome graphics that show you which action or view needs some optimization.