Add enviroment variable SYNAPSE_CACHE_FACTOR, default it to 0.1

synapse/handlers/presence.py

@@ -130,6 +130,10 @@ class PresenceHandler(BaseHandler):
             for state in active_presence
         }
 
+        metrics.register_callback(
+            "user_to_current_state_size", lambda: len(self.user_to_current_state)
+        )
+
         now = self.clock.time_msec()
         for state in active_presence:
             self.wheel_timer.insert(

synapse/handlers/receipts.py

@@ -36,8 +36,6 @@ class ReceiptsHandler(BaseHandler):
         )
         self.clock = self.hs.get_clock()
 
-        self._receipt_cache = None
-
     @defer.inlineCallbacks
     def received_client_receipt(self, room_id, receipt_type, user_id,
                                 event_id):

synapse/util/caches/descriptors.py

@@ -28,6 +28,7 @@ from twisted.internet import defer
 
 from collections import OrderedDict
 
+import os
 import functools
 import inspect
 import threading
@@ -38,9 +39,14 @@ logger = logging.getLogger(__name__)
 _CacheSentinel = object()
 
 
+CACHE_SIZE_FACTOR = float(os.environ.get("SYNAPSE_CACHE_FACTOR", 0.1))
+
+
 class Cache(object):
 
     def __init__(self, name, max_entries=1000, keylen=1, lru=True, tree=False):
+        max_entries = int(max_entries * CACHE_SIZE_FACTOR)
+
         if lru:
             cache_type = TreeCache if tree else dict
             self.cache = LruCache(