Follow up for counting quota usage from placement

This addresses comments from the series:

  * Remove usage-specific info from docstring
  * Add note to nova-next job description "changelog"
  * Add info about data migration to config option help
  * Consolidate code under count_usage_from_placement conditional
  * Consolidate variables for checking data migration doneness
  * Remove hard-coded user_id and project_id from func test
  * Re-word code comment about checking data migration doneness

Related to blueprint count-quota-usage-from-placement

Change-Id: Ida2de9256fcc9e092fb9977b8ac067fc1472c316

.zuul.yaml

@@ -165,6 +165,7 @@
       TLS console proxy code in the libvirt driver.
       Starting in Stein, the job was changed to run with python 3 and enabled
       volume multi-attach testing.
+      Starting in Train, the job enabled counting quota usage from placement.
       Runs all tempest compute API and most scenario tests concurrently.
     run: playbooks/legacy/nova-next/run.yaml
     post-run: playbooks/legacy/nova-next/post.yaml

nova/conf/quota.py

@@ -332,6 +332,15 @@ consume quota usage for cores and ram. Note that because of this, it will be
 possible for a request to unshelve a server to be rejected if the user does not
 have enough quota available to support the cores and ram needed by the server
 to be unshelved.
+
+The ``populate_queued_for_delete`` and ``populate_user_id`` online data
+migrations must be completed before usage can be counted from placement. Until
+the data migration is complete, the system will fall back to legacy quota usage
+counting from cell databases depending on the result of an EXISTS database
+query during each quota check, if this configuration option is set to True.
+Operators who want to avoid the performance hit from the EXISTS queries should
+wait to set this configuration option to True until after they have completed
+their online data migrations via ``nova-manage db online_data_migrations``.
 """),
 ]
 

nova/objects/instance_mapping.py

@@ -417,10 +417,6 @@ class InstanceMappingList(base.ObjectListBase, base.NovaObject):
         not included in the count (deleted and SOFT_DELETED instances).
         Instances that are queued_for_deleted=None are not included in the
         count because we are not certain about whether or not they are deleted.
-        When counting quota usage, we will fall back on the legacy counting
-        method and count instances, cores, and ram from cell databases if any
-        unmigrated instance mappings (user_id=None or queued_for_delete=None)
-        are detected, to avoid using a potentially inaccurate count.
 
         :param context: The request context for database access
         :param project_id: The project_id to count across

nova/quota.py

@@ -1176,8 +1176,9 @@ def _server_group_count_members_by_user(context, group, user_id):
                 {'user': 'server_group_members': <count across user>}}
     """
     # Because server group members quota counting is not scoped to a project,
-    # but scoped to a particular InstanceGroup and user, we cannot filter our
-    # user_id/queued_for_delete populated check on project_id or user_id.
+    # but scoped to a particular InstanceGroup and user, we have no reasonable
+    # way of pruning down our migration check to only a subset of all instance
+    # mapping records.
     # So, we check whether user_id/queued_for_delete is populated for all
     # records and cache the result to prevent unnecessary checking once the
     # data migration has been completed.
@@ -1185,9 +1186,8 @@ def _server_group_count_members_by_user(context, group, user_id):
     if not UID_QFD_POPULATED_CACHE_ALL:
         LOG.debug('Checking whether user_id and queued_for_delete are '
                   'populated for all projects')
-        uid_qfd_populated = _user_id_queued_for_delete_populated(context)
-        if uid_qfd_populated:
-            UID_QFD_POPULATED_CACHE_ALL = True
+        UID_QFD_POPULATED_CACHE_ALL = _user_id_queued_for_delete_populated(
+            context)
 
     if UID_QFD_POPULATED_CACHE_ALL:
         count = objects.InstanceMappingList.get_count_by_uuids_and_user(
@@ -1308,13 +1308,12 @@ def _instances_cores_ram_count(context, project_id, user_id=None):
                 UID_QFD_POPULATED_CACHE_BY_PROJECT.add(project_id)
         else:
             uid_qfd_populated = True
-        if not uid_qfd_populated:
-            LOG.warning('Falling back to legacy quota counting method for '
-                        'instances, cores, and ram')
-
-    if CONF.quota.count_usage_from_placement and uid_qfd_populated:
-        return _instances_cores_ram_count_api_db_placement(context, project_id,
-                                                           user_id=user_id)
+        if uid_qfd_populated:
+            return _instances_cores_ram_count_api_db_placement(context,
+                                                               project_id,
+                                                               user_id=user_id)
+    LOG.warning('Falling back to legacy quota counting method for instances, '
+                'cores, and ram')
     return _instances_cores_ram_count_legacy(context, project_id,
                                              user_id=user_id)
 

nova/tests/functional/db/test_quota.py

@@ -196,7 +196,9 @@ class QuotaTestCase(test.NoDBTestCase):
         self.assertEqual(1536, count['user']['ram'])
 
     def test_user_id_queued_for_delete_populated(self):
-        ctxt = context.RequestContext('fake-user', 'fake-project')
+        ctxt = context.RequestContext(
+            test_instance_mapping.sample_mapping['user_id'],
+            test_instance_mapping.sample_mapping['project_id'])
 
         # One deleted or SOFT_DELETED instance with user_id=None, should not be
         # considered by the check.