Re: making relfilenodes 56 bits

On Sat, Sep 3, 2022 at 1:50 PM Dilip Kumar <dilipbalaut(at)gmail(dot)com> wrote:
>
> On Tue, Aug 30, 2022 at 9:23 PM Robert Haas <robertmhaas(at)gmail(dot)com> wrote:
>
> > 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.
>
> Right.
>
> > 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.
>
> So as of now, we have two open options 1) the current approach and
> what patch is following to use Oid as relfilenode for the system
> tables when initially created. 2) call
> pg_binary_upgrade_move_things_out_of_the_way() which force rewrite all
> the system tables.
>
> Another idea that I am not very sure how feasible is. Can we change
> the dump such that in binary upgrade mode it will not use template0 as
> a template database (in creating database command) but instead some
> new database as a template e.g. template-XYZ? And later for conflict
> checking, we will create this template-XYZ database on the new cluster
> and then we will perform all the conflict check (from all the
> databases of the old cluster) and rewrite operations on this database.
> And later all the databases will be created using template-XYZ as the
> template and all the rewriting stuff we have done is still intact.
> The problems I could think of are 1) only for a binary upgrade we will
> have to change the pg_dump. 2) we will have to use another database
> name as the reserved database name but what if that name is already in
> use in the previous cluster?

While we are still thinking on this issue, I have rebased the patch on
the latest head and fixed a couple of minor issues.

--
Regards,
Dilip Kumar
EnterpriseDB: http://www.enterprisedb.com