Make bdms querying in multiple cells use scatter-gather

[Surya Seetharaman]

Currently the "_get_instance_bdms_in_multiple_cells" function in extended_volumes runs sequentially and this affects the performance in case of large deployments (running a lot of cells) : https://github.com/openstack/nova/blob/master/nova/api/openstack/compute/extended_volumes.py#L50

So it would be nice to use the scatter_gather_cells function to do this operation in parallel.

Also apart from the performance scaling point of view, in case connection to a particular cell fails, it would be nice to have sentinels returned which is done by the scatter_gather_cells function. This helps when a cell is down.

[OpenStack Infra (hudson-openstack)]

Fix proposed to branch: master
Review: https://review.openstack.org/541246

[Surya Seetharaman (tssurya)]

This bug was opened following the discussion on IRC : http://eavesdrop.openstack.org/meetings/nova_cells/2018/nova_cells.2018-01-24-21.00.log.html#l-215

[OpenStack Infra (hudson-openstack)]

Reviewed: https://review.openstack.org/541246
Committed: https://git.openstack.org/cgit/openstack/nova/commit/?id=ea6757092df85b6cce38980ae5b7f54b76657e01
Submitter: Zuul
Branch: master

commit ea6757092df85b6cce38980ae5b7f54b76657e01
Author: Surya Seetharaman <email address hidden>
Date: Tue Feb 6 12:36:50 2018 +0100

    Make bdms querying in multi-cell use scatter-gather and ignore down cell

    This patch makes the querying of bdms from multiple cells in the
    _get_instance_bdms_in_multiple_cells function of extended_volumes use
    scatter_gather_cells thus making the process, parallel. It also adds
    warnings in case a cell is not available; which the operator can later
    tweak, if an exception needs to be raised. So for now, cells that are
    not reachable are ignored and it proceeds to the next cell.

    Change-Id: I0e05eb1e2ad37962968b79100bf4a96c7d6ddd8f
    Closes-Bug: #1747650

[OpenStack Infra (hudson-openstack)]

Fix proposed to branch: stable/queens
Review: https://review.openstack.org/543489

[OpenStack Infra (hudson-openstack)]

Reviewed: https://review.openstack.org/543489
Committed: https://git.openstack.org/cgit/openstack/nova/commit/?id=a564fe1ac260381e786202ec1ea4de903b9cadc0
Submitter: Zuul
Branch: stable/queens

commit a564fe1ac260381e786202ec1ea4de903b9cadc0
Author: Surya Seetharaman <email address hidden>
Date: Tue Feb 6 12:36:50 2018 +0100

    Make bdms querying in multi-cell use scatter-gather and ignore down cell

    This patch makes the querying of bdms from multiple cells in the
    _get_instance_bdms_in_multiple_cells function of extended_volumes use
    scatter_gather_cells thus making the process, parallel. It also adds
    warnings in case a cell is not available; which the operator can later
    tweak, if an exception needs to be raised. So for now, cells that are
    not reachable are ignored and it proceeds to the next cell.

    Change-Id: I0e05eb1e2ad37962968b79100bf4a96c7d6ddd8f
    Closes-Bug: #1747650
    (cherry picked from commit ea6757092df85b6cce38980ae5b7f54b76657e01)

[OpenStack Infra (hudson-openstack)]

This issue was fixed in the openstack/nova 17.0.0.0rc2 release candidate.

[OpenStack Infra (hudson-openstack)]

This issue was fixed in the openstack/nova 18.0.0.0b1 development milestone.