[YawningAngel]

If you want a database that is arbitrarily horizontally scalable, there aren't really good open source options.

As a former employee it isn't clear to me that Monzo couldn't have used boring stuff for a while and switched to C* or some equivalent later when it was genuinely needed, but it's worked well enough for them that I'm not inclined to critique the decision post hoc.

[trollied]

Their last outage worries me greatly.

[YawningAngel]

I think there's a clear critique of Cassandra in there, in that it shouldn't even be possible to configure nodes to serve data they don't have.

Monzo... It's very hard to say. I think based on the contents of the blog post they acted reasonably and competently (yeah, the test rollout was a badly designed test, but that's easy to say post hoc). The only fair basis for critiquing Monzo would be if they had notably more averages than is 'typical', and we don't have the data or conceptual framework required to do that. As a customer, I can't think of risks that Monzo exposes you to that aren't also present with other banks. I bank with them ¯\ _(ツ)_/¯