"Florian G. Pflug" <fgp(at)phlo(dot)org> writes:
> This guarantee enables a few optimizations. First, as you say in the
> comments, finding the largest xid when committing becomes trivial. But more
> important, if we can assume that the proc array xid cache is always
> sorted, we can get ride of the exclusive lock during subxact abort.
No, we can't, because subxact abort still has to advance latestCompletedXid.
regards, tom lane