Re: [PoC] pg_upgrade: allow to upgrade publisher node

> Few comments:
> 1) We will be able to override the value of max_slot_wal_keep_size by
> using --new-options like '--new-options  "-c
> max_slot_wal_keep_size=val"':
> +       /*
> +        * Use max_slot_wal_keep_size as -1 to prevent the WAL removal by the
> +        * checkpointer process.  If WALs required by logical replication slots
> +        * are removed, the slots are unusable.  This setting prevents the
> +        * invalidation of slots during the upgrade. We set this option when
> +        * cluster is PG17 or later because logical replication slots
> can only be
> +        * migrated since then. Besides, max_slot_wal_keep_size is
> added in PG13.
> +        */
> +       if (GET_MAJOR_VERSION(cluster->major_version) >= 1700)
> +               appendPQExpBufferStr(&pgoptions, " -c
> max_slot_wal_keep_size=-1");
>
> Should there be a check to throw an error if this option is specified
> or do we need some documentation that this option should not be
> specified?

I have tested the above scenario. We are able to override the
max_slot_wal_keep_size by using  '--new-options  "-c
max_slot_wal_keep_size=val"'. And also with some insert statements
during pg_upgrade, old WAL file were deleted and logical replication
slots were invalidated. Since the slots were invalidated replication
was not happening after the upgrade.

Thanks,
Shlok Kumar Kyal