put a cache on /state_ids

Instead just warn. This is a temporary workaround to allow
provisioning new Modular hosts.

See https://github.com/matrix-org/synapse/pull/6734
and https://github.com/matrix-org/synapse/issues/6696#issuecomment-575280941

Signed-off-by: Jason Robinson <jasonr@matrix.org>

synapse/federation/federation_server.py

@@ -95,6 +95,9 @@ class FederationServer(FederationBase):
         # We cache responses to state queries, as they take a while and often
         # come in waves.
         self._state_resp_cache = ResponseCache(hs, "state_resp", timeout_ms=30000)
+        self._state_ids_resp_cache = ResponseCache(
+            hs, "state_ids_resp", timeout_ms=30000
+        )
 
     async def on_backfill_request(
         self, origin: str, room_id: str, versions: List[str], limit: int
@@ -362,10 +365,16 @@ class FederationServer(FederationBase):
         if not in_room:
             raise AuthError(403, "Host not in room.")
 
+        resp = await self._state_ids_resp_cache.wrap(
+            (room_id, event_id), self._on_state_ids_request_compute, room_id, event_id,
+        )
+
+        return 200, resp
+
+    async def _on_state_ids_request_compute(self, room_id, event_id):
         state_ids = await self.handler.get_state_ids_for_pdu(room_id, event_id)
         auth_chain_ids = await self.store.get_auth_chain_ids(state_ids)
-
-        return 200, {"pdu_ids": state_ids, "auth_chain_ids": auth_chain_ids}
+        return {"pdu_ids": state_ids, "auth_chain_ids": auth_chain_ids}
 
     async def _on_context_state_request_compute(
         self, room_id: str, event_id: str

synapse/federation/transport/server.py

@@ -340,6 +340,12 @@ class BaseFederationServlet(object):
                 if origin:
                     with ratelimiter.ratelimit(origin) as d:
                         await d
+                        if request._disconnected:
+                            logger.warning(
+                                "client disconnected before we started processing "
+                                "request"
+                            )
+                            return -1, None
                         response = await func(
                             origin, content, request.args, *args, **kwargs
                         )

synapse/storage/engines/postgres.py

@@ -95,7 +95,7 @@ class PostgresEngine(BaseDatabaseEngine):
             errors.append("    - 'CTYPE' is set to %r. Should be 'C'" % (ctype,))
 
         if errors:
-            raise IncorrectDatabaseSetup(
+            logger.warning(
                 "Database is incorrectly configured:\n\n%s\n\n"
                 "See docs/postgres.md for more information." % ("\n".join(errors))
             )