Add some randomness to the user specified timeout on event streams to mitigate...

Add some randomness to the user specified timeout on event streams to mitigate against thundering herds problems

synapse/handlers/events.py

@@ -23,6 +23,7 @@ from synapse.events.utils import serialize_event
 from ._base import BaseHandler
 
 import logging
+import random
 
 
 logger = logging.getLogger(__name__)
@@ -72,6 +73,14 @@ class EventStreamHandler(BaseHandler):
             rm_handler = self.hs.get_handlers().room_member_handler
             room_ids = yield rm_handler.get_rooms_for_user(auth_user)
 
+            if timeout:
+                # If they've set a timeout set a minimum limit.
+                timeout = max(timeout, 500)
+
+                # Add some randomness to this value to try and mitigate against
+                # thundering herds on restart.
+                timeout = random.randint(int(timeout*0.9), int(timeout*1.1))
+
             with PreserveLoggingContext():
                 events, tokens = yield self.notifier.get_events_for(
                     auth_user, room_ids, pagin_config, timeout