[Bug 1742649] Re: map_instances default batch size is too small.

[Matt Riedemann]

This is a one time operation when you're upgrading to a cells v2
deployment, so while it's unfortunate it took this long in a large cloud
with several thousand instances, I'd consider this lower priority to
resolve with code at this point unless the change is trivial. Therefore
option 3, better documentation of the command and it's option itself, is
probably what I'd lean toward.

** Tags added: cells nova-manage

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https://bugs.launchpad.net/bugs/1742649

Title:
  map_instances default batch size is too small.

Status in Ubuntu Cloud Archive:
  New
Status in OpenStack Compute (nova):
  Opinion
Status in nova package in Ubuntu:
  New

Bug description:
  Description
  ===========

  map_instances seemingly hung for hours on a cloud with ~190000
  instance records. I think the following fixes are valid (in order of
  preference):

  1) nova_manage should examine the amount of instances that need mapping and make an informed choice about batch size if max_count is not set.
  2) max_counts default should be raised. It is currently 50 and I cannot imagine what use case 50 is a good default for. For small clouds the max_count is almost irrelevant, for medium/large clouds 50 is far too low.
  3) Update max_count description. It currently reads "Maximum number of instances to map" but I think it should also point out that this is the batch size that instances will be processed in.

  Steps to reproduce
  ==================

  Fire up a large number of instances on a cloud and run map_instances
  without max_count set:

  nova-manage --config-file /etc/nova/nova.conf cell_v2 map_instances
  --cell_uuid <uuid>

  Expected result
  ===============

  The command should complete in a reasonable time (under an hour)

  Actual result
  =============

  Command runs for over three hours

  Environment
  ===========
  1. Exact version of OpenStack you are running. See the following
    list for all releases: http://docs.openstack.org/releases/

     If this is from a distro please provide

  # dpkg -l | grep nova
  ii  nova-api-os-compute              2:16.0.3-0ubuntu1~cloud0                   all          OpenStack Compute - OpenStack Compute API frontend
  ii  nova-common                      2:16.0.3-0ubuntu1~cloud0                   all          OpenStack Compute - common files
  ii  nova-conductor                   2:16.0.3-0ubuntu1~cloud0                   all          OpenStack Compute - conductor service
  ii  nova-placement-api               2:16.0.3-0ubuntu1~cloud0                   all          OpenStack Compute - placement API frontend
  ii  nova-scheduler                   2:16.0.3-0ubuntu1~cloud0                   all          OpenStack Compute - virtual machine scheduler
  ii  python-nova                      2:16.0.3-0ubuntu1~cloud0                   all          OpenStack Compute Python libraries

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