Given that most application developers started with something like a postgresql, or a MySQL that has pessimistic locking, and thus transactions rarely end in read / write conflicts (aborts), how have people (and potentially programming languages) adapted to optimistic concurrency control?

Also, when you say:

> On the other hand, server-side transactions use a more typical pessimistic relational lock. They open a transaction, do some work, and then commit it.

What do you mean? What are server-side transactions?