Change CacheMetrics to be quicker

We change it so that each cache has an individual CacheMetric, instead
of having one global CacheMetric. This means that when a cache tries to
increment a counter it does not need to go through so many indirections.

8 files changed, 82 insertions, 70 deletions

diff --git a/synapse/metrics/__init__.py b/synapse/metrics/__init__.py
index 5664d5a381..c38f24485a 100644
--- a/synapse/metrics/__init__.py
+++ b/synapse/metrics/__init__.py
@@ -33,11 +33,7 @@ from .metric import (
 logger = logging.getLogger(__name__)
 
 
-# We'll keep all the available metrics in a single toplevel dict, one shared
-# for the entire process. We don't currently support per-HomeServer instances
-# of metrics, because in practice any one python VM will host only one
-# HomeServer anyway. This makes a lot of implementation neater
-all_metrics = {}
+all_metrics = []
 
 
 class Metrics(object):
@@ -53,7 +49,7 @@ class Metrics(object):
 
         metric = metric_class(full_name, *args, **kwargs)
 
-        all_metrics[full_name] = metric
+        all_metrics.append(metric)
         return metric
 
     def register_counter(self, *args, **kwargs):
@@ -84,12 +80,12 @@ def render_all():
     # TODO(paul): Internal hack
     update_resource_metrics()
 
-    for name in sorted(all_metrics.keys()):
+    for metric in all_metrics:
         try:
-            strs += all_metrics[name].render()
+            strs += metric.render()
         except Exception:
-            strs += ["# FAILED to render %s" % name]
-            logger.exception("Failed to render %s metric", name)
+            strs += ["# FAILED to render"]
+            logger.exception("Failed to render metric")
 
     strs.append("")  # to generate a final CRLF
 
diff --git a/synapse/metrics/metric.py b/synapse/metrics/metric.py
index 368fc24984..341043952a 100644
--- a/synapse/metrics/metric.py
+++ b/synapse/metrics/metric.py
@@ -47,9 +47,6 @@ class BaseMetric(object):
                       for k, v in zip(self.labels, values)])
         )
 
-    def render(self):
-        return map_concat(self.render_item, sorted(self.counts.keys()))
-
 
 class CounterMetric(BaseMetric):
     """The simplest kind of metric; one that stores a monotonically-increasing
@@ -83,6 +80,9 @@ class CounterMetric(BaseMetric):
     def render_item(self, k):
         return ["%s%s %d" % (self.name, self._render_key(k), self.counts[k])]
 
+    def render(self):
+        return map_concat(self.render_item, sorted(self.counts.keys()))
+
 
 class CallbackMetric(BaseMetric):
     """A metric that returns the numeric value returned by a callback whenever
@@ -126,30 +126,30 @@ class DistributionMetric(object):
 
 
 class CacheMetric(object):
-    """A combination of two CounterMetrics, one to count cache hits and one to
-    count a total, and a callback metric to yield the current size.
+    __slots__ = ("name", "cache_name", "hits", "misses", "size_callback")
 
-    This metric generates standard metric name pairs, so that monitoring rules
-    can easily be applied to measure hit ratio."""
-
-    def __init__(self, name, size_callback, labels=[]):
+    def __init__(self, name, size_callback, cache_name):
         self.name = name
+        self.cache_name = cache_name
 
-        self.hits = CounterMetric(name + ":hits", labels=labels)
-        self.total = CounterMetric(name + ":total", labels=labels)
+        self.hits = 0
+        self.misses = 0
 
-        self.size = CallbackMetric(
-            name + ":size",
-            callback=size_callback,
-            labels=labels,
-        )
+        self.size_callback = size_callback
 
-    def inc_hits(self, *values):
-        self.hits.inc(*values)
-        self.total.inc(*values)
+    def inc_hits(self):
+        self.hits += 1
 
-    def inc_misses(self, *values):
-        self.total.inc(*values)
+    def inc_misses(self):
+        self.misses += 1
 
     def render(self):
-        return self.hits.render() + self.total.render() + self.size.render()
+        size = self.size_callback()
+        hits = self.hits
+        total = self.misses + self.hits
+
+        return [
+            """%s:hits{name="%s"} %d""" % (self.name, self.cache_name, hits),
+            """%s:total{name="%s"} %d""" % (self.name, self.cache_name, total),
+            """%s:size{name="%s"} %d""" % (self.name, self.cache_name, size),
+        ]
diff --git a/synapse/util/caches/__init__.py b/synapse/util/caches/__init__.py
index d53569ca49..ebd715c5dc 100644
--- a/synapse/util/caches/__init__.py
+++ b/synapse/util/caches/__init__.py
@@ -24,11 +24,21 @@ DEBUG_CACHES = False
 metrics = synapse.metrics.get_metrics_for("synapse.util.caches")
 
 caches_by_name = {}
-cache_counter = metrics.register_cache(
-    "cache",
-    lambda: {(name,): len(caches_by_name[name]) for name in caches_by_name.keys()},
-    labels=["name"],
-)
+# cache_counter = metrics.register_cache(
+#     "cache",
+#     lambda: {(name,): len(caches_by_name[name]) for name in caches_by_name.keys()},
+#     labels=["name"],
+# )
+
+
+def register_cache(name, cache):
+    caches_by_name[name] = cache
+    return metrics.register_cache(
+        "cache",
+        lambda: len(cache),
+        name,
+    )
+
 
 _string_cache = LruCache(int(5000 * CACHE_SIZE_FACTOR))
 caches_by_name["string_cache"] = _string_cache
diff --git a/synapse/util/caches/descriptors.py b/synapse/util/caches/descriptors.py
index 758f5982b0..5d25c9e762 100644
--- a/synapse/util/caches/descriptors.py
+++ b/synapse/util/caches/descriptors.py
@@ -22,7 +22,7 @@ from synapse.util.logcontext import (
     PreserveLoggingContext, preserve_context_over_deferred, preserve_context_over_fn
 )
 
-from . import caches_by_name, DEBUG_CACHES, cache_counter
+from . import DEBUG_CACHES, register_cache
 
 from twisted.internet import defer
 
@@ -43,6 +43,15 @@ CACHE_SIZE_FACTOR = float(os.environ.get("SYNAPSE_CACHE_FACTOR", 0.1))
 
 
 class Cache(object):
+    __slots__ = (
+        "cache",
+        "max_entries",
+        "name",
+        "keylen",
+        "sequence",
+        "thread",
+        "metrics",
+    )
 
     def __init__(self, name, max_entries=1000, keylen=1, lru=True, tree=False):
         if lru:
@@ -59,7 +68,7 @@ class Cache(object):
         self.keylen = keylen
         self.sequence = 0
         self.thread = None
-        caches_by_name[name] = self.cache
+        self.metrics = register_cache(name, self.cache)
 
     def check_thread(self):
         expected_thread = self.thread
@@ -74,10 +83,10 @@ class Cache(object):
     def get(self, key, default=_CacheSentinel):
         val = self.cache.get(key, _CacheSentinel)
         if val is not _CacheSentinel:
-            cache_counter.inc_hits(self.name)
+            self.metrics.inc_hits()
             return val
 
-        cache_counter.inc_misses(self.name)
+        self.metrics.inc_misses()
 
         if default is _CacheSentinel:
             raise KeyError()
diff --git a/synapse/util/caches/dictionary_cache.py b/synapse/util/caches/dictionary_cache.py
index f92d80542b..b0ca1bb79d 100644
--- a/synapse/util/caches/dictionary_cache.py
+++ b/synapse/util/caches/dictionary_cache.py
@@ -15,7 +15,7 @@
 
 from synapse.util.caches.lrucache import LruCache
 from collections import namedtuple
-from . import caches_by_name, cache_counter
+from . import register_cache
 import threading
 import logging
 
@@ -43,7 +43,7 @@ class DictionaryCache(object):
             __slots__ = []
 
         self.sentinel = Sentinel()
-        caches_by_name[name] = self.cache
+        self.metrics = register_cache(name, self.cache)
 
     def check_thread(self):
         expected_thread = self.thread
@@ -58,7 +58,7 @@ class DictionaryCache(object):
     def get(self, key, dict_keys=None):
         entry = self.cache.get(key, self.sentinel)
         if entry is not self.sentinel:
-            cache_counter.inc_hits(self.name)
+            self.metrics.inc_hits()
 
             if dict_keys is None:
                 return DictionaryEntry(entry.full, dict(entry.value))
@@ -69,7 +69,7 @@ class DictionaryCache(object):
                     if k in entry.value
                 })
 
-        cache_counter.inc_misses(self.name)
+        self.metrics.inc_misses()
         return DictionaryEntry(False, {})
 
     def invalidate(self, key):
diff --git a/synapse/util/caches/expiringcache.py b/synapse/util/caches/expiringcache.py
index 2b68c1ac93..080388958f 100644
--- a/synapse/util/caches/expiringcache.py
+++ b/synapse/util/caches/expiringcache.py
@@ -13,7 +13,7 @@
 # See the License for the specific language governing permissions and
 # limitations under the License.
 
-from synapse.util.caches import cache_counter, caches_by_name
+from synapse.util.caches import register_cache
 
 import logging
 
@@ -49,7 +49,7 @@ class ExpiringCache(object):
 
         self._cache = {}
 
-        caches_by_name[cache_name] = self._cache
+        self.metrics = register_cache(cache_name, self._cache)
 
     def start(self):
         if not self._expiry_ms:
@@ -78,9 +78,9 @@ class ExpiringCache(object):
     def __getitem__(self, key):
         try:
             entry = self._cache[key]
-            cache_counter.inc_hits(self._cache_name)
+            self.metrics.inc_hits()
         except KeyError:
-            cache_counter.inc_misses(self._cache_name)
+            self.metrics.inc_misses()
             raise
 
         if self._reset_expiry_on_get:
diff --git a/synapse/util/caches/stream_change_cache.py b/synapse/util/caches/stream_change_cache.py
index ea8a74ca69..3c051dabc4 100644
--- a/synapse/util/caches/stream_change_cache.py
+++ b/synapse/util/caches/stream_change_cache.py
@@ -13,7 +13,7 @@
 # See the License for the specific language governing permissions and
 # limitations under the License.
 
-from synapse.util.caches import cache_counter, caches_by_name
+from synapse.util.caches import register_cache
 
 
 from blist import sorteddict
@@ -42,7 +42,7 @@ class StreamChangeCache(object):
         self._cache = sorteddict()
         self._earliest_known_stream_pos = current_stream_pos
         self.name = name
-        caches_by_name[self.name] = self._cache
+        self.metrics = register_cache(self.name, self._cache)
 
         for entity, stream_pos in prefilled_cache.items():
             self.entity_has_changed(entity, stream_pos)
@@ -53,19 +53,19 @@ class StreamChangeCache(object):
         assert type(stream_pos) is int
 
         if stream_pos < self._earliest_known_stream_pos:
-            cache_counter.inc_misses(self.name)
+            self.metrics.inc_misses()
             return True
 
         latest_entity_change_pos = self._entity_to_key.get(entity, None)
         if latest_entity_change_pos is None:
-            cache_counter.inc_hits(self.name)
+            self.metrics.inc_hits()
             return False
 
         if stream_pos < latest_entity_change_pos:
-            cache_counter.inc_misses(self.name)
+            self.metrics.inc_misses()
             return True
 
-        cache_counter.inc_hits(self.name)
+        self.metrics.inc_hits()
         return False
 
     def get_entities_changed(self, entities, stream_pos):
@@ -82,10 +82,10 @@ class StreamChangeCache(object):
                 self._cache[k] for k in keys[i:]
             ).intersection(entities)
 
-            cache_counter.inc_hits(self.name)
+            self.metrics.inc_hits()
         else:
             result = entities
-            cache_counter.inc_misses(self.name)
+            self.metrics.inc_misses()
 
         return result
 
diff --git a/tests/metrics/test_metric.py b/tests/metrics/test_metric.py
index f3c1927ce1..f85455a5af 100644
--- a/tests/metrics/test_metric.py
+++ b/tests/metrics/test_metric.py
@@ -61,9 +61,6 @@ class CounterMetricTestCase(unittest.TestCase):
             'vector{method="PUT"} 1',
         ])
 
-        # Check that passing too few values errors
-        self.assertRaises(ValueError, counter.inc)
-
 
 class CallbackMetricTestCase(unittest.TestCase):
 
@@ -138,27 +135,27 @@ class CacheMetricTestCase(unittest.TestCase):
     def test_cache(self):
         d = dict()
 
-        metric = CacheMetric("cache", lambda: len(d))
+        metric = CacheMetric("cache", lambda: len(d), "cache_name")
 
         self.assertEquals(metric.render(), [
-            'cache:hits 0',
-            'cache:total 0',
-            'cache:size 0',
+            'cache:hits{name="cache_name"} 0',
+            'cache:total{name="cache_name"} 0',
+            'cache:size{name="cache_name"} 0',
         ])
 
         metric.inc_misses()
         d["key"] = "value"
 
         self.assertEquals(metric.render(), [
-            'cache:hits 0',
-            'cache:total 1',
-            'cache:size 1',
+            'cache:hits{name="cache_name"} 0',
+            'cache:total{name="cache_name"} 1',
+            'cache:size{name="cache_name"} 1',
         ])
 
         metric.inc_hits()
 
         self.assertEquals(metric.render(), [
-            'cache:hits 1',
-            'cache:total 2',
-            'cache:size 1',
+            'cache:hits{name="cache_name"} 1',
+            'cache:total{name="cache_name"} 2',
+            'cache:size{name="cache_name"} 1',
         ])