This comment seems needlessly rude.

How did you manage to make that a “millennial” thing

I think the point he's trying to make is that even with a selection of highly "en vogue" PaaS and frameworks, you still run up against basic problems in Computer Science, and that all the fancy frameworks can actually obfuscate the source of the problem. The sentiment seems to be "perhaps you could have done this with basic tools and not made the error, rather than using something trendy".

And millenial ~= trendy.

That's rude and arrogant.

No PaaS provider costs their DB instances on number of selects...

Perhaps you're the Junior developer?!

Pretty much every PaaS provider does that. If you're exceeding the number of queries a node can process you either need a bigger node or more nodes, therefore the amount you have to pay is directly related to the number of queries you send. The only difference is that firebase automatically adds more nodes behind the scenes which makes surprise bills possible. If you're not adding more nodes, your application simply stops serving requests reliably because your DB is overloaded. Therefore the actual problem is not the billing model, it's the fact that the code is crap.

From TFA: "Firebase, however, charges based on per 100k — 250k read, write and delete requests to the database."