Re: making relfilenodes 56 bits

On Tue, Aug 30, 2022 at 8:45 AM Dilip Kumar <dilipbalaut@gmail.com> wrote:
> I have found one more issue with this approach of rewriting the
> conflicting table.  Earlier I thought we could do the conflict
> checking and rewriting inside create_new_objects() right before the
> restore command.  But after implementing (while testing) this I
> realized that we DROP and CREATE the database while restoring the dump
> that means it will again generate the conflicting system tables.  So
> theoretically the rewriting should go in between the CREATE DATABASE
> and restoring the object but as of now both create database and
> restoring other objects are part of a single dump file.  I haven't yet
> analyzed how feasible it is to generate the dump in two parts, first
> part just to create the database and in second part restore the rest
> of the object.
>
> Thoughts?

Well, that's very awkward. It doesn't seem like it would be very
difficult to teach pg_upgrade to call pg_restore without --clean and
just do the drop database itself, but that doesn't really help,
because pg_restore will in any event be creating the new database.
That doesn't seem like something we can practically refactor out,
because only pg_dump knows what properties to use when creating the
new database. What we could do is have the dump include a command like
SELECT pg_binary_upgrade_move_things_out_of_the_way(some_arguments_here),
but that doesn't really help very much, because passing the whole list
of relfilenode values from the old database seems pretty certain to be
a bad idea. The whole idea here was that we'd be able to build a hash
table on the new database's system table OIDs, and it seems like
that's not going to work.

We could try to salvage some portion of the idea by making
pg_binary_upgrade_move_things_out_of_the_way() take a more restricted
set of arguments, like the smallest and largest relfilenode values
from the old database, and then we'd just need to move things that
overlap. But that feels pretty hit-or-miss to me as to whether it
actually avoids any work, and
pg_binary_upgrade_move_things_out_of_the_way() might also be annoying
to write. So perhaps we have to go back to the drawing board here.

-- 
Robert Haas
EDB: http://www.enterprisedb.com