On Wed, Jan 05, 2022 at 06:51:37PM -0500, Bruce Momjian wrote: > On Tue, Jan 4, 2022 at 10:22:50PM +0000, Finnerty, Jim wrote: > > I'm concerned about the maintainability impact of having 2 new > > on-disk page formats. It's already complex enough with XIDs and > > multixact-XIDs. > > > > If the lack of space for the two epochs in the special data area is > > a problem only in an upgrade scenario, why not resolve the problem > > before completing the upgrade process like a kind of post-process > > pg_repack operation that converts all "double xmax" pages to > > the "double-epoch" page format? i.e. maybe the "double xmax" > > representation is needed as an intermediate representation during > > upgrade, but after upgrade completes successfully there are no pages > > with the "double-xmax" representation. This would eliminate a whole > > class of coding errors and would make the code dealing with 64-bit > > XIDs simpler and more maintainable. > > Well, yes, we could do this, and it would avoid the complexity of having > to support two XID representations, but we would need to accept that > fast pg_upgrade would be impossible in such cases, since every page > would need to be checked and potentially updated. > > You might try to do this while the server is first started and running > queries, but I think we found out from the online checkpoint patch that
I think you meant the online checksum patch. Which this reminded me of, too. https://commitfest.postgresql.org/31/2611/ > having the server in an intermediate state while running queries is very > complex --- it might be simpler to just accept two XID formats all the > time than enabling the server to run with two formats for a short > period. My big point is that this needs more thought. -- Justin
