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[James Page <james.page@xxxxxxxxxx>]

** Also affects: nova (Ubuntu Vivid)
   Importance: Undecided
       Status: In Progress

** Also affects: nova (Ubuntu Utopic)
   Importance: Undecided
       Status: New

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https://bugs.launchpad.net/bugs/1388077

Title:
  Parallel periodic instance power state reporting from compute nodes
  has high impact on conductors and message broker

Status in OpenStack Compute (Nova):
  In Progress
Status in nova package in Ubuntu:
  In Progress
Status in nova source package in Utopic:
  New
Status in nova source package in Vivid:
  In Progress

Bug description:
  Environment: OpenStack Juno release/Ubuntu 14.04/480 compute nodes/8
  cloud controllers/40,000 instances +

  The change made in:

  https://github.com/openstack/nova/commit/baabab45e0ae0e9e35872cae77eb04bdb5ee0545

  switches power state reporting from being a serial process for each
  instance on a hypervisor to being a parallel thread for every
  instance; for clouds running high instance counts, this has quite an
  impact on the conductor processes as they try to deal with N instance
  refresh calls in parallel where N is the number of instances running
  on the cloud.

  It might be better to throttle this to a configurable parallel level
  so that period RPC load can be managed effectively in a larger cloud,
  or to continue todo this process in series but outside of the main
  thread.

  The net result of this activity is that it places increase demands on
  the message broker, which has to deal with more parallel connections,
  and the conductors as they try to consume all of the RPC requests; if
  the message broker hits its memory high water mark it will stop
  publishers publishing any more messages until the memory usage drops
  below the high water mark again - this might not be achievable if all
  conductor processes are tied up with existing RPC calls try to send
  replies, resulting in a message broker lockup and collapse of all RPC
  in the cloud.

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