PX COORDINATOR FORCED SERIAL

This is just a short heads-up for those that come across an execution plan showing the PX COORDINATOR FORCED SERIAL operation. I don't have official confirmation but according to my tests a plan with such an operation effectively means: Cost for parallel execution but execute serially (You might remember that I've recently mentioned in another post that there is the possibility to have a plan executed in parallel but costed serially, weird isn't it). Why such an operation exists is not clear to me - obviously it would make much more sense to cost straight away for serial execution in such a case. Probably there is a good reason, otherwise such an operation didn't exist but I think at least the costing is questionable in current versions.