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

On Fri, Sep 22, 2023 at 12:11 PM Amit Kapila <amit(dot)kapila16(at)gmail(dot)com> wrote:
>
> Yeah, both by tests and manually verifying the WAL records. Basically,
> we need to care about records that could be generated by background
> processes like checkpointer/bgwriter or can be generated during system
> table scans. You may want to read my latest email for a summary on how
> we reached at this design choice [1].
>
> [1] - https://www.postgresql.org/message-id/CAA4eK1JVKZGRHLOEotWi%2Be%2B09jucNedqpkkc-Do4dh5FTAU%2B5w%40mail.gmail.com

+ /* Logical slots can be migrated since PG17. */
+ if (GET_MAJOR_VERSION(old_cluster.major_version) <= 1600)
+ {

Why can't the patch allow migration of logical replication slots from
PG versions < 17 to say 17 or later? If done, it will be a main
advantage of the patch since it will enable seamless major version
upgrades of postgres database instances with logical replication
slots.

I'm looking at the changes to the postgres backend that this patch
does - AFICS, it does 2 things 1) implements
binary_upgrade_validate_wal_logical_end function, 2) adds an assertion
that the logical slots won't get invalidated. For (1), pg_upgrade can
itself can read the WAL from the old cluster to determine the logical
WAL end (i.e. implement the functionality of
binary_upgrade_validate_wal_logical_end ) because the xlogreader is
available to FRONTEND tools. For (2), it's just an assertion and
logical WAL end determining logic will anyway determine whether or not
the slots are valid; if needed, the assertion can be backported.

Is there anything else that stops this patch from supporting migration
of logical replication slots from PG versions < 17?

--
Bharath Rupireddy
PostgreSQL Contributors Team
RDS Open Source Databases
Amazon Web Services: https://aws.amazon.com