Re: optimize file transfer in pg_upgrade

On Wed, Mar 5, 2025 at 2:42 PM Nathan Bossart <nathandbossart@gmail.com> wrote:
> Of course, rollback would still be possible, but you'd really need to
> understand what "swap" mode does behind the scenes to do so safely.  In any
> case, I'm growing skeptical that a probably-not-super-well-tested script
> that extremely few people will need and fewer will use is worth the
> complexity.

I don't have a super-strong view on what the right thing to do is
here, but I'm definitely in favor of not doing something half-baked.
If you think the revert script is going to suck, then let's not have
it at all and just be clear about what the requirements for using this
mode are.

One serious danger that you didn't mention here is that, if pg_upgrade
does fail, you may well try several times. And if you forget the
revert script at some point, or run it more than once, or run the
wrong version, you will be in trouble. I feel like this is something
someone could very easily mess up even if in theory it works
perfectly. Upgrades are often stressful times.

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