Comment 6 for bug 1542491

your considering make lots of sense, and they are common issues in distributed system,
OpenStack use timestamp update method all over the codes like:
https://github.com/openstack/nova/blob/master/nova/scheduler/host_manager.py#L185
for your considering:
#1, synchronized timing is a basic assumption in distributed system like OS, even it make system prone to going wrong.
#2, timestamp is from DB operation, as long as mutli nova-api service operate to same single DB, this won't be a problem.
#3, very helpful heads up, the logic will be updating cache as long as DB timestamps = cache timestamps.