[Rpm-ecosystem] [Rpm-maint] RFC: Relocate RPM and DNF databases to /usr

[Florian Weimer]

* Colin Walters:

> On Wed, Dec 15, 2021, at 5:34 PM, Florian Weimer wrote:
>> * Chris Murphy:
>>
>>> Fedora 36 seems like a good time to do this. What do you think?
>>
>> It's a bit odd to locate a database under /usr that isn't pre-built and
>> installed.  
>
> Why is that odd?

Mentally, I still associate /usr with something that can be mounted
read-only from shared storage.

>> I guess in theory there could be systems with a read-only
>> /usr out there that still allow installation of packages into /opt.
>>
>> Does it really help to improve the snapshot situation? 
>
> Yes.  
>
> I didn't wake up one day and say "hey you know what, today I'm going
> to move the rpm database just for fun".  Neither, for that matter did
> the OpenSUSE folks.  We haven't had this conversation over and over
> throughout the years just because it was some minor thing.
>
> What I *did* wake up one day and say I'm going to do is make upgrades
> transactional and offline by default and hence safe.  No one should
> ever fear starting an operating system upgrade while their laptop is
> at 30% battery.  Administrators running important servers must be able
> to easily roll back when the kernel *or* systemd (or something) else
> regresses, because it's software, it regresses all the time despite
> our best efforts.

I appreciate these efforts.

Although transactional-update (as documented below) seems have one major
regression: transactional RPM updates now require reboots. 8-(

> So yes again, this does matter.  And it matters because whether you're
> doing "image based upgrades" like ostree or just "client side offline
> updates" like the
> https://kubic.opensuse.org/documentation/man-pages/transactional-update.8.html
> thing - it's very important *what data specifically* is
> versioned/snapshotted and what isn't.  On an ostree system for
> example, it's completely normal that there are *two* rpm databases
> (one you're running, one that's pending in the new root).
>
> All the data in the rpmdb is about content that's in `/usr`.

That totally ignores Software Collections and packages from ISVs.  If
the expected future that RPM is going to be an OS-internal software
deployment mechanism (and not be used for third-party software), it
should not be a side effect of this change, but an explicit decision.

Thanks,
Florian