Rename CacheCounterMetric to just CacheMetric; add a CallbackMetric component to give the size of the cache

synapse/metrics/__init__.py

@@ -15,7 +15,7 @@
 
 import logging
 
-from .metric import CounterMetric, CallbackMetric, CacheCounterMetric
+from .metric import CounterMetric, CallbackMetric, CacheMetric
 
 
 logger = logging.getLogger(__name__)
@@ -57,10 +57,10 @@ class Metrics(object):
 
         return metric
 
-    def register_cachecounter(self, name, *args, **kwargs):
+    def register_cache(self, name, *args, **kwargs):
         full_name = "%s.%s" % (self.name_prefix, name)
 
-        metric = CacheCounterMetric(full_name, *args, **kwargs)
+        metric = CacheMetric(full_name, *args, **kwargs)
 
         self._register(metric)
 

synapse/metrics/metric.py

@@ -76,19 +76,24 @@ class CallbackMetric(BaseMetric):
         # TODO(paul): work out something we can do with keys and vectors
         return ["%s %d" % (self.name, self.callback())]
 
-class CacheCounterMetric(object):
+class CacheMetric(object):
     """A combination of two CounterMetrics, one to count cache hits and one to
-    count misses.
+    count misses, and a callback metric to yield the current size.
 
     This metric generates standard metric name pairs, so that monitoring rules
     can easily be applied to measure hit ratio."""
 
-    def __init__(self, name, keys=[]):
+    def __init__(self, name, size_callback, keys=[]):
         self.name = name
 
         self.hits   = CounterMetric(name + ":hits",   keys=keys)
         self.misses = CounterMetric(name + ":misses", keys=keys)
 
+        self.size = CallbackMetric(name + ":size",
+            callback=size_callback,
+            keys=keys,
+        )
+
     def inc_hits(self, *values):
         self.hits.inc(*values)
 
@@ -96,4 +101,4 @@ class CacheCounterMetric(object):
         self.misses.inc(*values)
 
     def render(self):
-        return self.hits.render() + self.misses.render()
+        return self.hits.render() + self.misses.render() + self.size.render()

synapse/storage/_base.py

@@ -59,7 +59,7 @@ def cached(max_entries=1000):
     def wrap(orig):
         cache = OrderedDict()
 
-        counter = metrics.register_cachecounter(orig.__name__)
+        counter = metrics.register_cache(orig.__name__, lambda: len(cache))
 
         def prefill(key, value):
             while len(cache) > max_entries:
@@ -183,8 +183,8 @@ class SQLBaseStore(object):
         self._get_event_counters = PerformanceCounters()
 
         self._get_event_cache = LruCache(hs.config.event_cache_size)
-        self._get_event_cache_counter = metrics.register_cachecounter(
-            "get_event"
+        self._get_event_cache_counter = metrics.register_cache("get_event",
+            size_callback=lambda: len(self._get_event_cache),
         )
 
     def start_profiling(self):

tests/metrics/test_metric.py

@@ -16,7 +16,7 @@
 from tests import unittest
 
 from synapse.metrics.metric import (
-    CounterMetric, CallbackMetric, CacheCounterMetric
+    CounterMetric, CallbackMetric, CacheMetric
 )
 
 
@@ -81,26 +81,32 @@ class CallbackMetricTestCase(unittest.TestCase):
         ])
 
 
-class CacheCounterMetricTestCase(unittest.TestCase):
+class CacheMetricTestCase(unittest.TestCase):
 
-    def test_cachecounter(self):
-        counter = CacheCounterMetric("cache")
+    def test_cache(self):
+        d = dict()
 
-        self.assertEquals(counter.render(), [
+        metric = CacheMetric("cache", lambda: len(d))
+
+        self.assertEquals(metric.render(), [
             "cache:hits 0",
             "cache:misses 0",
+            "cache:size 0",
         ])
 
-        counter.inc_misses()
+        metric.inc_misses()
+        d["key"] = "value"
 
-        self.assertEquals(counter.render(), [
+        self.assertEquals(metric.render(), [
             "cache:hits 0",
             "cache:misses 1",
+            "cache:size 1",
         ])
 
-        counter.inc_hits()
+        metric.inc_hits()
 
-        self.assertEquals(counter.render(), [
+        self.assertEquals(metric.render(), [
             "cache:hits 1",
             "cache:misses 1",
+            "cache:size 1",
         ])