[Bug 1742649] Related fix merged to nova (master)

[OpenStack Infra]

Reviewed:  https://review.openstack.org/536959
Committed: https://git.openstack.org/cgit/openstack/nova/commit/?id=2890d8db67012d7c33c40a1e36a66766740b8f8f
Submitter: Zuul
Branch:    master

commit 2890d8db67012d7c33c40a1e36a66766740b8f8f
Author: Matt Riedemann <mriedem.os at gmail.com>
Date:   Tue Jan 23 15:30:47 2018 -0500

    Expand on when you might want to set --max-count for map_instances
    
    The default behavior for the "nova-manage cell_v2 map_instances"
    command is to map all instances in the cell in batches of 50.
    
    This can be slow when there are several thousand instances in the
    deployment and an operator may want to specify a higher --max-count
    value and run the command until it completes.
    
    This simply updates the command option description and man page to
    point this out for consideration.
    
    Change-Id: I59c2ed89fe02212977445f6825c6da8fedbb8ccf
    Related-Bug: #1742649

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

Title:
  map_instances default batch size is too small.

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

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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