Expose statistics on extrems to prometheus (#5384)

tests/storage/test_event_metrics.py

@@ -0,0 +1,97 @@
+# -*- coding: utf-8 -*-
+# Copyright 2019 The Matrix.org Foundation C.I.C.
+#
+# Licensed under the Apache License, Version 2.0 (the 'License');
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#     http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an 'AS IS' BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+
+from synapse.metrics import REGISTRY
+from synapse.types import Requester, UserID
+
+from tests.unittest import HomeserverTestCase
+
+
+class ExtremStatisticsTestCase(HomeserverTestCase):
+    def test_exposed_to_prometheus(self):
+        """
+        Forward extremity counts are exposed via Prometheus.
+        """
+        room_creator = self.hs.get_room_creation_handler()
+
+        user = UserID("alice", "test")
+        requester = Requester(user, None, False, None, None)
+
+        # Real events, forward extremities
+        events = [(3, 2), (6, 2), (4, 6)]
+
+        for event_count, extrems in events:
+            info = self.get_success(room_creator.create_room(requester, {}))
+            room_id = info["room_id"]
+
+            last_event = None
+
+            # Make a real event chain
+            for i in range(event_count):
+                ev = self.create_and_send_event(room_id, user, False, last_event)
+                last_event = [ev]
+
+            # Sprinkle in some extremities
+            for i in range(extrems):
+                ev = self.create_and_send_event(room_id, user, False, last_event)
+
+        # Let it run for a while, then pull out the statistics from the
+        # Prometheus client registry
+        self.reactor.advance(60 * 60 * 1000)
+        self.pump(1)
+
+        items = list(
+            filter(
+                lambda x: x.name == "synapse_forward_extremities",
+                list(REGISTRY.collect()),
+            )
+        )
+
+        # Check the values are what we want
+        buckets = {}
+        _count = 0
+        _sum = 0
+
+        for i in items[0].samples:
+            if i[0].endswith("_bucket"):
+                buckets[i[1]['le']] = i[2]
+            elif i[0].endswith("_count"):
+                _count = i[2]
+            elif i[0].endswith("_sum"):
+                _sum = i[2]
+
+        # 3 buckets, 2 with 2 extrems, 1 with 6 extrems (bucketed as 7), and
+        # +Inf which is all
+        self.assertEqual(
+            buckets,
+            {
+                1.0: 0,
+                2.0: 2,
+                3.0: 0,
+                5.0: 0,
+                7.0: 1,
+                10.0: 0,
+                15.0: 0,
+                20.0: 0,
+                50.0: 0,
+                100.0: 0,
+                200.0: 0,
+                500.0: 0,
+                "+Inf": 3,
+            },
+        )
+        # 3 rooms, with 10 total events
+        self.assertEqual(_count, 3)
+        self.assertEqual(_sum, 10)