> So what’s a good web app datastore in your opinion, if SQL is highly overrated?

I've used Cassandra very successfully, but there are plenty of options.

> > Storing old data as-is

> What does this mean? Can you give an example?

I mean not migrating the stored version of old data (note I'm not suggesting "no schema" or anything like that; what I'm opposing is the idea that you have a single global mutable version of the schema and mutate historical records in place to match that). E.g. if you started by storing users with a single nationality field and then realised that actually the same user can have multiple nationalities, while you'd change the DTO representation of a user that you read into, you wouldn't rewrite the on-disk representation of previously stored users.