Re: A recent message added to pg_upgade

On Fri, Oct 27, 2023 at 2:02 PM Alvaro Herrera <alvherre@alvh.no-ip.org> wrote:
>
> On 2023-Oct-27, Kyotaro Horiguchi wrote:
>
> > @@ -1433,8 +1433,8 @@ InvalidatePossiblyObsoleteSlot(ReplicationSlotInvalidationCause cause,
> >               {
> >                       ereport(ERROR,
> >                                       errcode(ERRCODE_INVALID_PARAMETER_VALUE),
> > -                                     errmsg("replication slots must not be invalidated during the upgrade"),
> > -                                     errhint("\"max_slot_wal_keep_size\" must be set to -1 during the upgrade"));
>
> Hmm, if I read this code right, this error is going to be thrown by the
> checkpointer while finishing a checkpoint.  Fortunately, the checkpoint
> record has already been written, but I don't know what would happen if
> this is thrown while trying to write the shutdown checkpoint.  Probably
> nothing terribly good.
>
> I don't think this is useful.  If the setting is invalid during binary
> upgrade, let's prevent it from being set at all right from the start of
> the upgrade process.

We are already forcing the required setting
"max_slot_wal_keep_size=-1" during the upgrade similar to some of the
other settings like "full_page_writes". However, the user can provide
an option for "max_slot_wal_keep_size" in which case it will be
overridden. Now, I think (a) we can ensure that our setting always
takes precedence in this case. The other idea is (b) to parse the
user-provided options and check if "max_slot_wal_keep_size" has a
value different than expected and raise an error accordingly. Or we
can simply (c) document the usage of max_slot_wal_keep_size in the
upgrade. I am not sure whether it is worth complicating the code for
this as the user shouldn't be using such an option during the upgrade.
So, I think doing (a) and (c) could be simpler.

>
>  In InvalidatePossiblyObsoleteSlot() we could have
> just an Assert() or elog(PANIC).
>

Yeah, we can change to either of those.

-- 
With Regards,
Amit Kapila.