If by persist to disk you mean "when you're done", it can by replicating the db to a file. Another option is to back it up over the network, e.g., https://github.com/benbjohnson/litestream

SQL is a very nice querying language, if you can stuff your data in it and run structured queries instead of some spaghetti code it can help a lot. This is the same domain as redis initially, ie a "database" with helpful structures and data types for simple data mangling

It's great for running tests in parallel.

Or for working with data in memory.

There's a whole world of software outside of saas crud