On Mon, Mar 01, 2021 at 04:32:23PM +0100, Hannu Krosing wrote: > It looks like we are unnecessarily instructing our usiers to vacuum their > databases in single-user mode when just vacuuming would be enough.
> When I started looking at improving the situation I discovered, that there > already is no need to run VACUUM in single user mode in any currently > supported > PostgreSQL version as you can run VACUUM perfectly well when the wraparound > protection is active. A comment in SetTransactionIdLimit() says, "VACUUM requires an XID if it truncates at wal_level!=minimal." Hence, I think plain VACUUM will fail some of the time; VACUUM (TRUNCATE false) should be reliable. In general, I like your goal of replacing painful error message advice with less-painful advice. At the same time, it's valuable for the advice to reliably get the user out of the bad situation.
