For the record, I think this will be a disaster. There is far too much code that will get broken, largely silently, and much of it is not under our control.
While I've long been in favor of a multi-threaded implementation, now in my old age, I tend to agree with Tom. I'd be interested in Konstantin's thoughts (and PostgresPro's experience) of multi-threaded vs. internal pooling with the current process-based model. I recall looking at and playing with Konstantin's implementations of both, which were impressive. Yes, the latter doesn't solve the same issues, but many real-world ones where multi-threaded is argued. Personally, I think there would be not only a significant amount of time spent dealing with in-the-field stability regressions before a multi-threaded implementation matures, but it would also increase the learning curve for anyone trying to start with internals development.
