Merge "Cache database and message queue connection objects" into stable/newton

nova/context.py

@@ -34,6 +34,10 @@ from nova import policy
 from nova import utils
 
 LOG = logging.getLogger(__name__)
+# TODO(melwitt): This cache should be cleared whenever WSGIService receives a
+# SIGHUP and periodically based on an expiration time. Currently, none of the
+# cell caches are purged, so neither is this one, for now.
+CELL_CACHE = {}
 
 
 class _ContextAuthPlugin(plugin.BaseAuthPlugin):
@@ -349,11 +353,27 @@ def target_cell(context, cell_mapping):
     :param context: The RequestContext to add connection information
     :param cell_mapping: A objects.CellMapping object
     """
+    global CELL_CACHE
+
     original_db_connection = context.db_connection
     # avoid circular import
     from nova import db
-    db_connection_string = cell_mapping.database_connection
-    context.db_connection = db.create_context_manager(db_connection_string)
+
+    # Synchronize access to the cache by multiple API workers.
+    @utils.synchronized(cell_mapping.uuid)
+    def get_or_set_cached_cell_and_set_connections():
+        try:
+            cell_db_conn = CELL_CACHE[cell_mapping.uuid]
+        except KeyError:
+            db_connection_string = cell_mapping.database_connection
+            context.db_connection = db.create_context_manager(
+                db_connection_string)
+            CELL_CACHE[cell_mapping.uuid] = context.db_connection
+        else:
+            context.db_connection = cell_db_conn
+
+    get_or_set_cached_cell_and_set_connections()
+
     try:
         yield context
     finally:

nova/test.py

@@ -211,6 +211,9 @@ class TestCase(testtools.TestCase):
         self.useFixture(conf_fixture.ConfFixture(CONF))
         self.useFixture(nova_fixtures.RPCFixture('nova.test'))
 
+        # NOTE(melwitt): Reset the cached db connection objects
+        context.CELL_CACHE = {}
+
         if self.USES_DB:
             self.useFixture(nova_fixtures.Database())
             self.useFixture(nova_fixtures.Database(database='api'))

nova/tests/unit/test_context.py

@@ -20,6 +20,7 @@ from nova import context
 from nova import exception
 from nova import objects
 from nova import test
+from nova.tests import uuidsentinel as uuids
 
 
 class ContextTestCase(test.NoDBTestCase):
@@ -286,7 +287,26 @@ class ContextTestCase(test.NoDBTestCase):
                                       roles=['admin', 'weasel'])
         # Verify the existing db_connection, if any, is restored
         ctxt.db_connection = mock.sentinel.db_conn
-        mapping = objects.CellMapping(database_connection='fake://')
+        mapping = objects.CellMapping(database_connection='fake://',
+                                      transport_url='fake://',
+                                      uuid=uuids.cell)
         with context.target_cell(ctxt, mapping):
             self.assertEqual(ctxt.db_connection, mock.sentinel.cm)
         self.assertEqual(mock.sentinel.db_conn, ctxt.db_connection)
+
+    @mock.patch('nova.db.create_context_manager')
+    def test_target_cell_caching(self, mock_create_cm):
+        mock_create_cm.return_value = mock.sentinel.db_conn_obj
+        ctxt = context.RequestContext('111', '222')
+        mapping = objects.CellMapping(database_connection='fake://db',
+                                      transport_url='fake://mq',
+                                      uuid=uuids.cell)
+        # First call should create new connection objects.
+        with context.target_cell(ctxt, mapping):
+            self.assertEqual(mock.sentinel.db_conn_obj, ctxt.db_connection)
+        mock_create_cm.assert_called_once_with('fake://db')
+        # Second call should use cached objects.
+        mock_create_cm.reset_mock()
+        with context.target_cell(ctxt, mapping):
+            self.assertEqual(mock.sentinel.db_conn_obj, ctxt.db_connection)
+        mock_create_cm.assert_not_called()

releasenotes/notes/bug-1691545-1acd6512effbdffb.yaml

@@ -0,0 +1,10 @@
+---
+fixes:
+  - |
+    Fixes `bug 1691545`_ in which there was a significant increase in database
+    connections because of the way connections to cell databases were being
+    established. With this fix, objects related to database connections are
+    cached in the API service and reused to prevent new connections being
+    established for every communication with cell databases.
+
+    .. _bug 1691545: https://bugs.launchpad.net/nova/+bug/1691545