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Reviewed:  https://review.openstack.org/263399
Committed: https://git.openstack.org/cgit/openstack/nova/commit/?id=d0ff6363d477da3be179e77d9958e6c8f09b459d
Submitter: Jenkins
Branch:    master

commit d0ff6363d477da3be179e77d9958e6c8f09b459d
Author: Matt Riedemann <mriedem@xxxxxxxxxx>
Date:   Mon Jan 4 11:21:01 2016 -0800

    libvirt: only get instance.flavor if needed in get_disk_mapping
    
    When attaching a volume, the compute API gets the instance
    with the default extra fields, which does not include flavor.
    
    So get_disk_mapping is lazy-loading the flavor in this case just
    to get the swap information from the flavor, which is only done
    if it's not already in the block_device_info dict passed in.
    
    So this change simply moves the instance.get_flavor() call to
    where it's needed to avoid a potentially unnecessary round-trip
    to the database to lazy-load the instance.flavor attribute.
    
    Change-Id: I316c3a917fcd8ac543c7990657fdfeb96f9a2eb8
    Closes-Bug: #1530952


** Changed in: nova
       Status: In Progress => Fix Released

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https://bugs.launchpad.net/bugs/1530952

Title:
  libvirt: should only lazy-load flavor from instance in
  get_disk_mapping if necessary

Status in OpenStack Compute (nova):
  Fix Released

Bug description:
  Debugging a failure I see this several times in the logs:

  http://logs.openstack.org/07/263207/1/check/gate-manila-tempest-dsvm-
  neutron-no-share-servers-
  multibackend/6717bb8/logs/screen-n-cpu.txt.gz#_2016-01-04_11_17_18_679

  2016-01-04 11:17:18.679 DEBUG nova.objects.instance [req-
  576413dd-8271-4110-995a-e6b828dc3035 nova service] Lazy-loading
  `flavor' on Instance uuid b4e9b1a0-77c7-4bde-9413-e14dfe7e3601
  obj_load_attr /opt/stack/new/nova/nova/objects/instance.py:843

  This is happening when attaching a volume to the instance and it's
  trying to determine the device to use for the mountpoint.

  The instance is retrieved in the API and by default it doesn't include
  the flavor attribute (which is a join on another table).

  This code is lazy-loading the flavor attribute on the instance, which
  with remote conductor is a round trip over rpc to conductor to get the
  flavor from the database and store it back on the instance:

  https://github.com/openstack/nova/blob/07ba7619f2d13c5ef6fe89252a7349acd84dcd9e/nova/virt/libvirt/blockinfo.py#L522

  And this is only used if the block_device_info doesn't have any swap
  information in it:

  https://github.com/openstack/nova/blob/07ba7619f2d13c5ef6fe89252a7349acd84dcd9e/nova/virt/libvirt/blockinfo.py#L579

  So we should avoid the round-trip to conductor and not lazy-load the
  flavor if we can, which means only getting it if that first condition
  fails (no swap info in the block_device_info).

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