** Changed in: nova
Status: Fix Committed => Fix Released
** Changed in: nova
Milestone: None => liberty-rc1
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https://bugs.launchpad.net/bugs/1385489
Title:
ResourceTracker._update_usage_from_migrations() is inefficient due to
multiple Instance.get_by_uuid() lookups
Status in OpenStack Compute (nova):
Fix Released
Bug description:
Here is our ResourceTracker._update_usage_from_migration() code:
def _update_usage_from_migrations(self, context, resources,
migrations):
self.tracked_migrations.clear()
filtered = {}
# do some defensive filtering against bad migrations records in the
# database:
for migration in migrations:
instance = migration['instance']
if not instance:
# migration referencing deleted instance
continue
uuid = instance['uuid']
# skip migration if instance isn't in a resize state:
if not self._instance_in_resize_state(instance):
LOG.warn(_("Instance not resizing, skipping migration."),
instance_uuid=uuid)
continue
# filter to most recently updated migration for each instance:
m = filtered.get(uuid, None)
if not m or migration['updated_at'] >= m['updated_at']:
filtered[uuid] = migration
for migration in filtered.values():
instance = migration['instance']
try:
self._update_usage_from_migration(context, instance, None,
resources, migration)
except exception.FlavorNotFound:
LOG.warn(_("Flavor could not be found, skipping "
"migration."), instance_uuid=uuid)
continue
Unfortunately, when the migration object's 'instance' attribute is
accessed, a call across RPC and DB occurs:
https://github.com/openstack/nova/blob/stable/icehouse/nova/objects/migration.py#L77-L80
@property
def instance(self):
return instance_obj.Instance.get_by_uuid(self._context,
self.instance_uuid)
For some very strange reason, the code in
_update_usage_from_migration() builds a "filtered"dictionary with the
migration objects that need to be accounted for in the resource
usages, and then once it builds that filtered dictionary, it goes
through the values and calls _update_usage_from_migration(), passing
the migration object's instance object.
There's no reason to do this at all. The filtered variable can go away
and the call to _update_usage_from_migration() can occur in the main
for loop, using the same instance variable from the original line:
instance = migration['instance']
That way, for each migration, we don't need to do two lookup by UUID
calls through the conductor to get the migration's instance object...
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