On Mon, May 1, 2023 at 9:16 AM Peter Geoghegan <p...@bowt.ie> wrote: > On Mon, May 1, 2023 at 9:08 AM Robert Haas <robertmh...@gmail.com> wrote: > > I disagree. If you start the cluster in single-user mode, you can > > actually wrap it around, unless something has changed that I don't > > know about. > > This patch relies on John's other patch which strongly discourages the > use of single-user mode. Were it not for that, I might agree.
Also, it's not clear that the term "wraparound" even describes what happens when you corrupt the database by violating the "no more than ~2.1 billion XIDs distance between any two unfrozen XIDs" invariant in single-user mode. What specific thing will have wrapped around? It's possible (and very likely) that every unfrozen XID in the database is from the same 64-XID-wise epoch. I don't think that we need to say very much about this scenario (and nothing at all about the specifics in "Routine Vacuuming"), so maybe it doesn't matter much. But I maintain that it makes most sense to describe this scenario as a violation of the "no more than ~2.1 billion XIDs distance between any two unfrozen XIDs" invariant, while leaving the term "wraparound" out of it completely. That terms has way too much baggage. -- Peter Geoghegan
