By ismail 
4 days ago Rails v6.0.0.rc1 was released. This means new version will be released in a few weeks, this is important, because new version includes some performance improvements and the performance is everything for apps.
In the beginning of this year (2019) I’ve started to work on legacy rails app that is version v5.0 and it was working nice on powerful Virtual Private Server (VPS) stand alone. As you know VPS is hard to manage for developers, you should create DevOps team to manage this complexity. For this reason I’ve moved to app to Heroku. I’ve used all Heroku resources like Heroku Postgres, Heroku Redis and looked metrics. It was really slow than VPS when a lot of people use the app at the same time even if I use Performance M or L dynos and powerful Postgres. There was some connection bottle necks in database side.
Later I started to upgrade project one level up stable release versions (Rails 5.0 to 5.2 and Ruby 2.4.3 to 2.5.3). Changes has been deployed to server on 21.th February, as you see below image, there was significant changing in db connection count after this update.
It decreased connection count almost %75. This was amazing for me.
So keep updated your rails and ruby versions for better performance.