I think this shows how counting on horizontal scaling to handle inefficiency only works for a while, and will eventually introduce its own set of complexities -

I think this shows how counting on horizontal scaling to handle inefficiency only works for a while, and will eventually introduce its own set of complexities - and dealing with those might be more trouble than coding things more efficiently in the first place. Then again, maybe it's worth it for a huge company like Shopify, because they save work for the feature devs by adding extra load on the test infrastructure devs, effectively increasing developer parallelism. Finally I wonder if they could have done more to speed up their tests? I'm maintaining a Rails codebase too, and I cut test time down by two thirds by rewriting tests with efficiency in mind - e.g. by ignoring dogma like 'each test needs to run completely independently of previous ones' (if I verify the state between tests, do I really need to pay the performance penalty of a database wipe?) The test-prof gem has a great tool, let-it-be, that allows you to designate db state that should not get wiped between tests. That and focusing on more unit tests and fewer integration test has really gone a long way toward speeding things up again for me.