timer: skip projects not using the pipeline

This change makes the timer driver skip projects that are not configured
to use the timer triggered pipeline. Timer operates on branch heads and
doesn't need speculative layouts to decide if it should be enqueued or not.
So it can be decided on cached data if it needs to run or not.

Change-Id: I410c0da5057727734ac82ce56cad75655a9ebc40

releasenotes/notes/timer-optimization-a6babecaf1c7dab8.yaml

@@ -0,0 +1,6 @@
+---
+fixes:
+  - |
+    The timer trigger does not enqueue an event for every branch of every
+    project anymore and it now only processes projects actually using the
+    pipeline triggered by a timer.

tests/fixtures/layouts/timer.yaml

@@ -39,6 +39,12 @@
           label: ubuntu-xenial
     run: playbooks/project-bitrot.yaml
 
+- project:
+    name: org/project1
+    check:
+      jobs:
+        - project-test1
+
 - project:
     name: org/project
     check:

tests/unit/test_scheduler.py

@@ -3375,6 +3375,18 @@ class TestScheduler(ZuulTestCase):
 
         self.assertEqual(len(self.builds), 2)
 
+        merge_count_project1 = 0
+        for job in self.gearman_server.jobs_history:
+            if job.name == b'merger:refstate':
+                args = job.arguments
+                if isinstance(args, bytes):
+                    args = args.decode('utf-8')
+                args = json.loads(args)
+                if args["items"][0]["project"] == "org/project1":
+                    merge_count_project1 += 1
+        self.assertEquals(merge_count_project1, 0,
+                          "project1 shouldn't have any refstate call")
+
         self.executor_server.hold_jobs_in_build = False
         # Stop queuing timer triggered jobs so that the assertions
         # below don't race against more jobs being queued.

zuul/driver/timer/__init__.py

@@ -79,7 +79,13 @@ class TimerDriver(Driver, TriggerInterface):
                     jobs.append(job)
 
     def _onTrigger(self, tenant, pipeline_name, timespec):
-        for project_name in tenant.layout.project_configs.keys():
+        for project_name, pcs in tenant.layout.project_configs.items():
+            # timer operates on branch heads and doesn't need speculative
+            # layouts to decide if it should be enqueued or not.
+            # So it can be decided on cached data if it needs to run or not.
+            if not [True for pc in pcs if pipeline_name in pc.pipelines]:
+                continue
+
             (trusted, project) = tenant.getProject(project_name)
             for branch in project.source.getProjectBranches(project, tenant):
                 event = TimerTriggerEvent()