Log which cache is throwing exceptions

synapse/util/caches/__init__.py

@@ -13,6 +13,7 @@
 # See the License for the specific language governing permissions and
 # limitations under the License.
 
+import logging
 import os
 
 import six
@@ -20,6 +21,8 @@ from six.moves import intern
 
 from prometheus_client.core import REGISTRY, Gauge, GaugeMetricFamily
 
+logger = logging.getLogger(__name__)
+
 CACHE_SIZE_FACTOR = float(os.environ.get("SYNAPSE_CACHE_FACTOR", 0.5))
 
 
@@ -76,6 +79,7 @@ def register_cache(cache_type, cache_name, cache):
             return []
 
         def collect(self):
+            try:
                 if cache_type == "response_cache":
                     response_cache_size.labels(cache_name).set(len(cache))
                     response_cache_hits.labels(cache_name).set(self.hits)
@@ -86,6 +90,9 @@ def register_cache(cache_type, cache_name, cache):
                     cache_hits.labels(cache_name).set(self.hits)
                     cache_evicted.labels(cache_name).set(self.evicted_size)
                     cache_total.labels(cache_name).set(self.hits + self.misses)
+            except Exception as e:
+                logger.warn("Error calculating metrics for %s: %s", cache_name, e)
+                raise
 
             yield GaugeMetricFamily("__unused", "")