[smsm42]

"Difficult" doesn't even begin to do it justice. Making a code which has 2k global variables and probably order of magnitude as many underlying assumptions (the code should know that now every time you touch X you may be influenced or influence all other threads that may touch X) is a gargantuan task, and will absolutely for sure involve many iterations which any sane person would never let anywhere near valuable data (and how long would it take until you'd consider it safe enough?). And making this all performant - given that shared-state code requires completely different approach to thinking about workload distribution, something that performs when running in isolated processes may very well get bogged down in locking or cache races hell when sharing the state - would be even harder. I am not doubting Postgres has some very smart people - much, much smarter than me, in any case - but I'd say it could be more practical to write new core from scratch than trying to "refactor" the core that organically grew for decades with assumptions of share-nothing model.