Re: BUG #18979: pg_upgrade to PG17 fails if max_slot_wal_keep_size is not set to -1

On Sun, Jul 6, 2025 at 8:26 AM Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> wrote:

> PG Bug reporting form <noreply(at)postgresql(dot)org> writes:
>
> > Expected Behavior:
> > pg_upgrade should automatically override max_slot_wal_keep_size to -1 as
> > required for upgrade mode.
>
> I do not think it is within pg_upgrade's charter to modify your
> postgresql.conf file.
>

That isn't what is being asked. They simply want the override that is
already in place to actually work.

> However, maybe instead of having check_max_slot_wal_keep_size
> throw an error about this, we could make it just silently keep
> the value as -1. There's a nearby thread about silently ignoring
> inappropriate GUC settings during initdb [1], and this seems like
> it'd be in the same spirit. Or we could just drop the server-side
> check altogether, figuring that it's pg_upgrade's job to see to
> that.
>

Can't we just move this to postmaster.c ~ line 850 ?

This seems no different than wal_level and summarize_wal having a
co-dependency such that intermediate invalid states must be allowed to
exist so long as what the server ends up running under is valid.
max_slot_wal_keep_size is sighup just like summarize_wal
(and IsBinaryUpgrade behaves like a postmaster GUC)

David J.