allow configurable pipeline partitioning

existing code will create queues from the cartesian product of the
set of pipelines and the set of agents. these queues are identified
by pipe_type-pipe_name-agent_id. the problem arises where if an agent
dies, any messages left on it's queue will be lost as agent_id's tend
to be unique.

this patch changes the logic so rather than using the number of agents
as the set we build our cartesian product from, we use a set of numbers
of a configurable size. by default, it will be a set of 10 so that queues
are created from the product set of the set of pipelines and the set
{0, 1, 2, 3, ... 9}. similarly, the pipelines queues will be identified
by pipe_type-pipe_name-x, where x is value from numerical set. this
way, if an agent dies, the queues are still known and can be
redistributed and processed among the active agents.

Change-Id: I35e3afdd2c9f97ab5bc6bb89531bd20308c5f8c0
Closes-Bug: #1486754

ceilometer/notification.py

@@ -34,6 +34,12 @@ LOG = log.getLogger(__name__)
 
 
 OPTS = [
+    cfg.IntOpt('pipeline_processing_queues',
+               default=10,
+               min=1,
+               help='Number of queues to parallelize workload across. This '
+                    'value should be larger than the number of active '
+                    'notification agents for optimal results.'),
     cfg.BoolOpt('ack_on_event_error',
                 default=True,
                 deprecated_group='collector',
@@ -96,12 +102,12 @@ class NotificationService(service_base.BaseService):
 
     def _get_notifiers(self, transport, pipe):
         notifiers = []
-        for agent in self.partition_coordinator._get_members(self.group_id):
+        for x in range(cfg.CONF.notification.pipeline_processing_queues):
             notifiers.append(oslo_messaging.Notifier(
                 transport,
                 driver=cfg.CONF.publisher_notifier.telemetry_driver,
                 publisher_id='ceilometer.notification',
-                topic='%s-%s-%s' % (self.NOTIFICATION_IPC, pipe.name, agent)))
+                topic='%s-%s-%s' % (self.NOTIFICATION_IPC, pipe.name, x)))
         return notifiers
 
     def _get_pipe_manager(self, transport, pipeline_manager):
@@ -238,20 +244,24 @@ class NotificationService(service_base.BaseService):
             ev_pipes = self.event_pipeline_manager.pipelines
         pipelines = self.pipeline_manager.pipelines + ev_pipes
         transport = messaging.get_transport()
-        for pipe in pipelines:
-            LOG.debug('Pipeline endpoint: %s', pipe.name)
-            pipe_endpoint = (pipeline.EventPipelineEndpoint
-                             if isinstance(pipe, pipeline.EventPipeline) else
-                             pipeline.SamplePipelineEndpoint)
-            listener = messaging.get_notification_listener(
-                transport,
-                [oslo_messaging.Target(
-                    topic='%s-%s-%s' % (self.NOTIFICATION_IPC,
-                                        pipe.name,
-                                        self.partition_coordinator._my_id))],
-                [pipe_endpoint(self.ctxt, pipe)])
-            listener.start()
-            self.pipeline_listeners.append(listener)
+        partitioned = self.partition_coordinator.extract_my_subset(
+            self.group_id,
+            range(cfg.CONF.notification.pipeline_processing_queues))
+        for pipe_set in partitioned:
+            for pipe in pipelines:
+                LOG.debug('Pipeline endpoint: %s from set: %s', pipe.name,
+                          pipe_set)
+                pipe_endpoint = (pipeline.EventPipelineEndpoint
+                                 if isinstance(pipe, pipeline.EventPipeline)
+                                 else pipeline.SamplePipelineEndpoint)
+                listener = messaging.get_notification_listener(
+                    transport,
+                    [oslo_messaging.Target(
+                        topic='%s-%s-%s' % (self.NOTIFICATION_IPC,
+                                            pipe.name, pipe_set))],
+                    [pipe_endpoint(self.ctxt, pipe)])
+                listener.start()
+                self.pipeline_listeners.append(listener)
 
     def stop(self):
         if self.partition_coordinator:

ceilometer/tests/functional/test_notification.py

@@ -390,9 +390,9 @@ class TestRealNotificationHA(BaseRealNotification):
 
     def test_reset_listeners_on_refresh(self):
         self.srv.start()
-        self.assertEqual(2, len(self.srv.pipeline_listeners))
+        self.assertEqual(20, len(self.srv.pipeline_listeners))
         self.srv._refresh_listeners()
-        self.assertEqual(2, len(self.srv.pipeline_listeners))
+        self.assertEqual(20, len(self.srv.pipeline_listeners))
         self.srv.stop()
 
     @mock.patch('oslo_messaging.Notifier.sample')
@@ -463,6 +463,8 @@ class TestRealNotificationMultipleAgents(tests_base.BaseTestCase):
                                group="notification")
         self.CONF.set_override('workload_partitioning', True,
                                group='notification')
+        self.CONF.set_override('pipeline_processing_queues', 2,
+                               group='notification')
         self.publisher = test_publisher.TestPublisher("")
         self.publisher2 = test_publisher.TestPublisher("")