What makes you think that it will require that many changes? There will be some widespread mechanical changes (which can be verified to be complete with a bit of low level work, like a script using objdump/nm to look for non-TLS mutable variables) and some areas changing more heavily (e.g. connection establishment, crash detection, signal handling, minor details of the locking code). But large portions of the code won't need to change. Note that we/postgres already shares a lot of state across processes.