Most of my tables have a column called “metadata”, “extra” or “ payload” with jsonb type… for the data i don’t want to model the rigid way.

It’s no longer relational vs. NoSQL, you can get the best of both worlds. Assuming of course you don’t need “planetscale”.

Nice, and by the looks of it you can still do joins to what is inside the jsonb. I presume indexes are possible too (or if not just pull that data out to actual columns).

Yup, it’s way more than a blob. You can query it.

Yeah it's postgres's jsonb type.

There are, but they’re pretty niche because their performance is really bad. Niche enough I can’t recall a single name today.

But really, my advice for early prototyping is split in two: either keep it in memory and serialize to disk, or use SQLite.

Note that even using serialized memory constructs will require data migrations, aka schema updates.

No contradiction at all. Imagine a relational database where the only column type is a variant (union) of the usual datatypes, and where new tables and new columns are auto-created whenever an insert/update references them (and, possibly, unused tables and columns are garbage-collected). You’d still use regular SQL and have joins and everything, the tables would still be relations, but there’s no defined schema.