Cache federation state responses

synapse/federation/federation_server.py

@@ -21,10 +21,11 @@ from .units import Transaction, Edu
 
 from synapse.util.async import Linearizer
 from synapse.util.logutils import log_function
+from synapse.util.caches.response_cache import ResponseCache
 from synapse.events import FrozenEvent
 import synapse.metrics
 
-from synapse.api.errors import FederationError, SynapseError
+from synapse.api.errors import AuthError, FederationError, SynapseError
 
 from synapse.crypto.event_signing import compute_event_signature
 
@@ -48,9 +49,15 @@ class FederationServer(FederationBase):
     def __init__(self, hs):
         super(FederationServer, self).__init__(hs)
 
+        self.auth = hs.get_auth()
+
         self._room_pdu_linearizer = Linearizer()
         self._server_linearizer = Linearizer()
 
+        # We cache responses to state queries, as they take a while and often
+        # come in waves.
+        self._state_resp_cache = ResponseCache(hs, timeout_ms=30000)
+
     def set_handler(self, handler):
         """Sets the handler that the replication layer will use to communicate
         receipt of new PDUs from other home servers. The required methods are
@@ -188,10 +195,29 @@ class FederationServer(FederationBase):
     @defer.inlineCallbacks
     @log_function
     def on_context_state_request(self, origin, room_id, event_id):
+        if not event_id:
+            raise NotImplementedError("Specify an event")
+
+        in_room = yield self.auth.check_host_in_room(room_id, origin)
+        if not in_room:
+            raise AuthError(403, "Host not in room.")
+
+        result = self._state_resp_cache.get((room_id, event_id))
+        if not result:
             with (yield self._server_linearizer.queue((origin, room_id))):
-            if event_id:
+                resp = yield self.response_cache.set(
+                    (room_id, event_id),
+                    self._on_context_state_request_compute(room_id, event_id)
+                )
+        else:
+            resp = yield result
+
+        defer.returnValue((200, resp))
+
+    @defer.inlineCallbacks
+    def _on_context_state_request_compute(self, room_id, event_id):
         pdus = yield self.handler.get_state_for_pdu(
-                    origin, room_id, event_id,
+            room_id, event_id,
         )
         auth_chain = yield self.store.get_auth_chain(
             [pdu.event_id for pdu in pdus]
@@ -208,8 +234,6 @@ class FederationServer(FederationBase):
                         self.hs.config.signing_key[0]
                     )
                 )
-            else:
-                raise NotImplementedError("Specify an event")
 
         defer.returnValue((200, {
             "pdus": [pdu.get_pdu_json() for pdu in pdus],

synapse/handlers/federation.py

@@ -991,14 +991,9 @@ class FederationHandler(BaseHandler):
         defer.returnValue(None)
 
     @defer.inlineCallbacks
-    def get_state_for_pdu(self, origin, room_id, event_id, do_auth=True):
+    def get_state_for_pdu(self, room_id, event_id):
         yield run_on_reactor()
 
-        if do_auth:
-            in_room = yield self.auth.check_host_in_room(room_id, origin)
-            if not in_room:
-                raise AuthError(403, "Host not in room.")
-
         state_groups = yield self.store.get_state_groups(
             room_id, [event_id]
         )

synapse/handlers/room.py

@@ -345,8 +345,8 @@ class RoomCreationHandler(BaseHandler):
 class RoomListHandler(BaseHandler):
     def __init__(self, hs):
         super(RoomListHandler, self).__init__(hs)
-        self.response_cache = ResponseCache()
-        self.remote_list_request_cache = ResponseCache()
+        self.response_cache = ResponseCache(hs)
+        self.remote_list_request_cache = ResponseCache(hs)
         self.remote_list_cache = {}
         self.fetch_looping_call = hs.get_clock().looping_call(
             self.fetch_all_remote_lists, REMOTE_ROOM_LIST_POLL_INTERVAL

synapse/handlers/sync.py

@@ -138,7 +138,7 @@ class SyncHandler(object):
         self.presence_handler = hs.get_presence_handler()
         self.event_sources = hs.get_event_sources()
         self.clock = hs.get_clock()
-        self.response_cache = ResponseCache()
+        self.response_cache = ResponseCache(hs)
 
     def wait_for_sync_for_user(self, sync_config, since_token=None, timeout=0,
                                full_state=False):

synapse/util/caches/response_cache.py

@@ -24,9 +24,12 @@ class ResponseCache(object):
     used rather than trying to compute a new response.
     """
 
-    def __init__(self):
+    def __init__(self, hs, timeout_ms=0):
         self.pending_result_cache = {}  # Requests that haven't finished yet.
 
+        self.clock = hs.get_clock()
+        self.timeout_sec = timeout_ms / 1000.
+
     def get(self, key):
         result = self.pending_result_cache.get(key)
         if result is not None:
@@ -39,6 +42,12 @@ class ResponseCache(object):
         self.pending_result_cache[key] = result
 
         def remove(r):
+            if self.timeout_sec:
+                self.clock.call_later(
+                    self.timeout_sec,
+                    self.pending_result_cache.pop, key, None,
+                )
+            else:
                 self.pending_result_cache.pop(key, None)
             return r