Don't update revision number if object was not modified

If there were not changes made to data in the database there is no
reason to bump revision numbers because the underlying drivers won't
change too. This saves cycles in case empty updates are incoming to the
API.

Co-Authored-By: Ihar Hrachyshka <[email protected]>

Closes-bug: #2065094
Change-Id: Ib74fdab7a8927ef9cc24ef7810e9cf2c264941eb
(cherry picked from commit 5795c19)

Author: cubeek

neutron/services/revisions/revision_plugin.py

@@ -78,14 +78,14 @@ def _get_objects_to_bump_revision(self, dirty_objects):
     def bump_revisions(self, session, context, instances):
         self._enforce_if_match_constraints(session)
         # bump revision number for updated objects in the session
+        modified_objs = {o for o in session.dirty if session.is_modified(o)}
         self._bump_obj_revisions(
-            session,
-            self._get_objects_to_bump_revision(session.dirty))
+            session, self._get_objects_to_bump_revision(modified_objs))
 
         # see if any created/updated/deleted objects bump the revision
         # of another object
         objects_with_related_revisions = [
-            o for o in session.deleted | session.dirty | session.new
+            o for o in modified_objs | set(session.deleted) | set(session.new)
             if getattr(o, 'revises_on_change', ())
         ]
         collected = session.info.setdefault('_related_bumped', set())

neutron/tests/unit/services/revisions/test_revision_plugin.py

@@ -143,13 +143,13 @@ def test_constrained_port_update_handles_db_retries(self):
         # update
         with self.port() as port:
             rev = port['port']['revision_number']
-            new = {'port': {'name': 'nigiri'}}
 
             def concurrent_increment(s):
                 db_api.sqla_remove(se.Session, 'before_commit',
                                    concurrent_increment)
                 # slip in a concurrent update that will bump the revision
                 plugin = directory.get_plugin()
+                new = {'port': {'name': 'nigiri'}}
                 plugin.update_port(nctx.get_admin_context(),
                                    port['port']['id'], new)
                 raise db_exc.DBDeadlock()
@@ -160,13 +160,16 @@ def concurrent_increment(s):
             # transaction, the revision number is tested only once the first
             # time the revision number service is executed for this session and
             # object.
+            new = {'port': {'name': 'sushi'}}
             self._update('ports', port['port']['id'], new,
                          headers={'If-Match': 'revision_number=%s' % rev},
                          expected_code=exc.HTTPOk.code)
+            new = {'port': {'name': 'salmon'}}
             self._update('ports', port['port']['id'], new,
                          headers={'If-Match': 'revision_number=%s' %
                                               str(int(rev) + 2)},
                          expected_code=exc.HTTPOk.code)
+            new = {'port': {'name': 'tea'}}
             self._update('ports', port['port']['id'], new,
                          headers={'If-Match': 'revision_number=1'},
                          expected_code=exc.HTTPPreconditionFailed.code)