populate_queued_for_delete queries the cell database for instances even if there are no instance mappings to migrate in that cell

[Matt Riedemann]

If we get here:

https://github.com/openstack/nova/blob/eb93d0cffd11fcfca97b3d4679a0043142a5d998/nova/objects/instance_mapping.py#L169

And the results are empty we can move on to the next cell without querying the cell database since we have nothing to migrate.

Also, the joinedload on cell_mapping here:

https://github.com/openstack/nova/blob/eb93d0cffd11fcfca97b3d4679a0043142a5d998/nova/objects/instance_mapping.py#L164

Is not used so could also be removed.

[OpenStack Infra (hudson-openstack)]

Fix proposed to branch: master
Review: https://review.openstack.org/639840

[OpenStack Infra (hudson-openstack)]

Reviewed: https://review.openstack.org/639840
Committed: https://git.openstack.org/cgit/openstack/nova/commit/?id=47061e699b9dbf6fdeea572a5abeaa72e499ec87
Submitter: Zuul
Branch: master

commit 47061e699b9dbf6fdeea572a5abeaa72e499ec87
Author: Matt Riedemann <email address hidden>
Date: Wed Feb 27 16:24:24 2019 -0500

    Optimize populate_queued_for_delete online data migration

    The data migration was needlessly querying the cell database
    for instances even if there were no instance mappings in that
    database that needed to be migrated. This simply continues to
    the next cell if the instance mappings in the current cell are
    migrated.

    While we're in here, the joinedload on 'cell_mapping' can be
    removed since it's not used.

    Closes-Bug: #1817961

    Change-Id: Idf35ed9d57945bc80fbd47393b7de076330160e6

[OpenStack Infra (hudson-openstack)]

This issue was fixed in the openstack/nova 19.0.0.0rc1 release candidate.