Andres Freund <and...@anarazel.de> writes: > On 2019-05-07 09:34:42 -0400, Tom Lane wrote: >> I'm inclined to wonder why bother with invals at all.
> But when updating the free space for the first four blocks, we're going > to either have to do an smgrexists() to check whether somebody > concurrently created the FSM, or we might not update an existing FSM. An > inval seems much better. I do not think sinval messaging is going to be sufficient to avoid that problem. sinval is only useful to tell you about changes if you first take a lock strong enough to guarantee that no interesting change is happening while you hold the lock. We are certainly not going to let writes take an exclusive lock, so I don't see how we could be certain that we've seen an sinval message telling us about FSM status change. This seems tied into the idea we've occasionally speculated about of tracking relation sizes in shared memory to avoid lseek calls. If we could solve the problems around that, it'd provide a cheap(er) way to detect whether an FSM should exist or not. A different way of looking at it is that the FSM data is imprecise by definition, therefore it doesn't matter that much if some backend is slow to realize that the FSM exists. That still doesn't lead me to think that sinval messaging is a component of the solution though. regards, tom lane