Comment 3 for bug 1567497

Reviewed: https://review.openstack.org/302792
Committed: https://git.openstack.org/cgit/openstack/neutron/commit/?id=e532ee3fccd0820f9ab0efc417ee787fb8c870e9
Submitter: Jenkins
Branch: master

commit e532ee3fccd0820f9ab0efc417ee787fb8c870e9
Author: Oleg Bondarev <email address hidden>
Date: Thu Apr 7 16:45:52 2016 +0300

    Notify resource_versions from agents only when needed

    resource_versions were included into agent state reports recently to
    support rolling upgrades (commit 97a272a892fcf488949eeec4959156618caccae8)
    The downside is that it brought additional processing when handling state
    reports on server side: update of local resources versions cache and
    more seriously rpc casts to all other servers to do the same.
    All this led to a visible performance degradation at scale with hundreds
    of agents constantly sending reports. Under load (rally test) agents
    may start "blinking" which makes cluster very unstable.

    In fact there is no need to send and update resource_versions in each state
    report. I see two cases when it should be done:
     1) agent was restarted (after it was upgraded);
     2) agent revived - which means that server was not receiving or being able
        to process state reports for some time (agent_down_time). During that
        time agent might be upgraded and restarted.

    So this patch makes agents include resource_versions info only on startup.
    After agent revival server itself will update version_manager with
    resource_versions taken from agent DB record - this is to avoid
    version_manager being outdated.

    Closes-Bug: #1567497
    Change-Id: I47a9869801f4e8f8af2a656749166b6fb49bcd3b