Robert Haas <robertmhaas@gmail.com> writes:
> Well, one long-running transaction that only has a single XID is not
> really a problem: the snapshot is still small. But one very old
> transaction that also happens to have a large number of
> subtransactions all of which have XIDs assigned might be a good way to
> stress the system.
That's a good point. If the ring buffer size creates a constraint on
the maximum number of sub-XIDs per transaction, you're going to need a
fallback path of some sort.
regards, tom lane