Not necessarily. What if it's recycled as a backend in a different postgres installation. Or just a cronjob or shell running as the same user? Sure, you can argue that the superuser can destroy anything he wants - but in that case, why do we have a check for this at all in the first place? I think we can safely say that any OS that actually manages to recycle the PID in the short time it takes to get between those instructions is so broken we don't need to care about that.