I wanted to summarize a series of changes which have improved the
performance of the NovaClusterDataModel builder for audits across single
and multiple cells (in the CERN case) by a factor of 20-30%.

There were initially three changes involved (in order):

1. https://review.opendev.org/#/c/659688/ - Optimize
NovaClusterDataModelCollector.add_instance_node

Reports on that patch alone said it fixed a regression introduced in
Stein with scoped audits:

"I checked this patch on the my test environment on the stable/stein
branch. I have more than 1000 virtual servers (some real, some dummy).
Previously, in the stable/rocky branch, the time to build a cluster was
about 15-20 minutes, in the Stein branch there was a regression and the
time increased to 90 minutes. After this patch, the build time is only 2
minutes."

That change was backported to stable/stein.

2. - https://review.opendev.org/#/c/661121/ - Optimize hypervisor API
calls (which requires https://review.opendev.org/#/c/659886/)

As noted that change requires a patch to python-novaclient if you are
looking to backport the change. We can't backport that upstream because
of the python-novaclient dependency since it would require bumping the
minimum required version of the library on a stable branch which is
against stable branch policy (minimum version of library dependencies
are more or less frozen on stable branches).

That change also requires configuring watcher with:

[nova_client]
api_version = 2.53  # or greater; train now requires at least 2.56

3. - https://review.opendev.org/#/c/662089/ - Optimize
NovaHelper.get_compute_node_by_hostname

This optimizes code used to build/update the nova CDM during
notification processing and also fixes a bug about looking up the
compute service properly.

After those three changes were merged, Corne Lukken (Dantali0n) started
doing scale and performance testing with and without the changes in a
CERN 5-cell test cluster. Corne identified a regression for which Canwei
Li determined the root cause and chenker fixed:

4. https://review.opendev.org/#/c/668100/ - Reduce the query time of the
instances when call get_instance_list()

With that fix applied Corne reported the overall improvement of 20-30%
when building the nova CDM during an audit in various scenarios. The
actual performance numbers will be sent later as part of a thesis Corne
is working on.

I want to thank Dantali0n, licanwei and chenker for all of their help
with this series of improvements.

--

Thanks,

Matt