Merge pull request #5461 from matrix-org/erikj/histograms_are_cumalitive

Prometheus histograms are cumalative

Author: erikjohnston

changelog.d/5461.feature

@@ -0,0 +1 @@
+Statistics on forward extremities per room are now exposed via Prometheus.

synapse/metrics/__init__.py

@@ -224,7 +224,6 @@ def collect(self):
             for i, bound in enumerate(self.buckets):
                 if x <= bound:
                     buckets[bound] = buckets.get(bound, 0) + data[x]
-                    break
 
         for i in self.buckets:
             res.append([str(i), buckets.get(i, 0)])

synapse/storage/events.py

@@ -228,7 +228,8 @@ def __init__(self, db_conn, hs):
         self._state_resolution_handler = hs.get_state_resolution_handler()
 
         # Collect metrics on the number of forward extremities that exist.
-        self._current_forward_extremities_amount = {}
+        # Counter of number of extremities to count
+        self._current_forward_extremities_amount = c_counter()
 
         BucketCollector(
             "synapse_forward_extremities",

tests/storage/test_event_metrics.py

@@ -64,16 +64,16 @@ def test_exposed_to_prometheus(self):
         expected = set([
             b'synapse_forward_extremities_bucket{le="1.0"} 0.0',
             b'synapse_forward_extremities_bucket{le="2.0"} 2.0',
-            b'synapse_forward_extremities_bucket{le="3.0"} 0.0',
-            b'synapse_forward_extremities_bucket{le="5.0"} 0.0',
-            b'synapse_forward_extremities_bucket{le="7.0"} 1.0',
-            b'synapse_forward_extremities_bucket{le="10.0"} 0.0',
-            b'synapse_forward_extremities_bucket{le="15.0"} 0.0',
-            b'synapse_forward_extremities_bucket{le="20.0"} 0.0',
-            b'synapse_forward_extremities_bucket{le="50.0"} 0.0',
-            b'synapse_forward_extremities_bucket{le="100.0"} 0.0',
-            b'synapse_forward_extremities_bucket{le="200.0"} 0.0',
-            b'synapse_forward_extremities_bucket{le="500.0"} 0.0',
+            b'synapse_forward_extremities_bucket{le="3.0"} 2.0',
+            b'synapse_forward_extremities_bucket{le="5.0"} 2.0',
+            b'synapse_forward_extremities_bucket{le="7.0"} 3.0',
+            b'synapse_forward_extremities_bucket{le="10.0"} 3.0',
+            b'synapse_forward_extremities_bucket{le="15.0"} 3.0',
+            b'synapse_forward_extremities_bucket{le="20.0"} 3.0',
+            b'synapse_forward_extremities_bucket{le="50.0"} 3.0',
+            b'synapse_forward_extremities_bucket{le="100.0"} 3.0',
+            b'synapse_forward_extremities_bucket{le="200.0"} 3.0',
+            b'synapse_forward_extremities_bucket{le="500.0"} 3.0',
             b'synapse_forward_extremities_bucket{le="+Inf"} 3.0',
             b'synapse_forward_extremities_count 3.0',
             b'synapse_forward_extremities_sum 10.0',