There's a very important metric they have left out of their data on settings for each test run: WEB_CONCURRENCY. While this will be different per app it will ma

There's a very important metric they have left out of their data on settings for each test run: WEB_CONCURRENCY. While this will be different per app it will make a big difference to the performance. They mention they had 67 processes on 10 p-large dynos, but why 67? Did they do some separate testing to prove that was optimal? In my experience it should be tested as an independent variable (to dyno number and type) to optimise performance. I will however 100% echo that it is never worth scaling on shared tenancy dynos. In my experience the combination of noisy neighbours and random routing means you'll very likely end up with worse performance by adding shared tenancy dynos.