> We use optimistic versioning, with a dedicated "version" field (that is actually always pulled out of the blob in all tables).

All well and good but you do need to handle failures elegantly in code. The nice thing about flat DB tables and SQL is you don't really have to care if your goal is to update a single column authoritatively. The state of the other values in the table are, often, immaterial. It gets even more complicated reconciling deeply nested conflicts in open schemas.

Not knocking your approach, it's just a trade-off I guess.

> A lot of high-level ORM frameworks simply save all the objects' fields on update, without doing fine-grained diffs.

Perhaps that is true... I'm a Rails dev and ActiveRecord definitely tracks mutations on the object and selectively updates.

I would assume this is consistent with Django and I'd assume a policy is probably required to be specified by SQLAlchemy.