Ronnie Sahlberg [off-list ref] writes:
Update receive-pack to use an atomic transaction iff the client negotiated
that it wanted atomic-push.
This leaves the default behavior to be the old non-atomic one ref at a
time update. This is to cause as little disruption as possible to existing
clients. It is unknown if there are client scripts that depend on the old
non-atomic behavior so we make it opt-in for now.
Later patch in this series also adds a configuration variable where you can
override the atomic push behavior on the receiving repo and force it
to use atomic updates always.
Nice.