One followup that should help people understand things:
When someone pushes an update to a package that isn't
in Atomic Host (or Workstation), *and* one is using rpm-ostree
in "pure ostree" mode (i.e. you never ran `rpm-ostree install`),
then checking for updates just uses libostree, which like any
sane image system, makes this a very cheap operation.
In the case of libostree, checking for "no changes" is just a few
HTTP requests for tiny files.
Say for example you've got a bunch of CentOS containers
on your FAH system (IMO this is not just a valid use case but
one I'd encourage) - you don't see an available update whenever
a new Firefox or whatever appears.
We were also doing ~two week batching for FAH updates before
Bodhi started doing batching...the interaction between those
really could be better...that's a whole other topic.
Anyways though to finish the explanation:
the second you do `rpm-ostree install libvirt` for example
(as I have done on my home server), you're doing *both* systems;
now libdnf comes into play, and it's the same RPM metadata from Fedora
with all the same performance penalty. Smoothing out this dramatic cliff of
a transition is part of the reason I'm working on rpm-ostree jigdo.