Remove system_metadata db calls from compute manager

The compute/manager makes several unnecessary db calls to fetch
the instance system_metadata, which is available in the instance
object itself now. This patch replaces those uses, avoiding the
need to farm them out to conductor.

Related to bp/no-db-compute
Related to bp/no-db-compute-manager

Change-Id: I26ff77be17eb538a4fcd238ffe52f8bde4fbe3e0

2 files changed, 12 insertions, 9 deletions

diff --git a/nova/compute/manager.py b/nova/compute/manager.py
index 295125f90..a1595320e 100644
--- a/nova/compute/manager.py
+++ b/nova/compute/manager.py
@@ -1048,9 +1048,9 @@ class ComputeManager(manager.SchedulerDependentManager):
                                          vm_state=vm_states.DELETED,
                                          task_state=None,
                                          terminated_at=timeutils.utcnow())
+        system_meta = compute_utils.metadata_to_dict(
+            instance['system_metadata'])
         self.db.instance_destroy(context, instance_uuid)
-        system_meta = self.db.instance_system_metadata_get(context,
-            instance_uuid)
 
         # ensure block device mappings are not leaked
         self.conductor_api.block_device_mapping_destroy(context, bdms)
@@ -1537,8 +1537,8 @@ class ComputeManager(manager.SchedulerDependentManager):
 
     def _get_rescue_image_ref(self, context, instance):
         """Determine what image should be used to boot the rescue VM. """
-        system_meta = self.db.instance_system_metadata_get(
-                context, instance['uuid'])
+        system_meta = compute_utils.metadata_to_dict(
+            instance['system_metadata'])
 
         rescue_image_ref = system_meta.get('image_base_image_ref')
 
diff --git a/nova/compute/utils.py b/nova/compute/utils.py
index a0dfbea8d..8852cb820 100644
--- a/nova/compute/utils.py
+++ b/nova/compute/utils.py
@@ -37,6 +37,13 @@ CONF.import_opt('host', 'nova.config')
 LOG = log.getLogger(__name__)
 
 
+def metadata_to_dict(metadata):
+    result = {}
+    for item in metadata:
+        result[item['key']] = item['value']
+    return result
+
+
 def add_instance_fault_from_exc(context, instance_uuid, fault, exc_info=None):
     """Adds the specified fault to the database."""
 
@@ -153,11 +160,7 @@ def notify_usage_exists(context, instance_ref, current_period=False,
             ignore_missing_network_data)
 
     if system_metadata is None:
-        try:
-            system_metadata = db.instance_system_metadata_get(
-                    context, instance_ref['uuid'])
-        except exception.NotFound:
-            system_metadata = {}
+        system_metadata = metadata_to_dict(instance_ref['system_metadata'])
 
     # add image metadata to the notification:
     image_meta = notifications.image_meta(system_metadata)