Fix 500 error on /messages when we accumulate more than 5 backward extremities

changelog.d/11027.bugfix

@@ -0,0 +1 @@
+Fix 500 error on `/messages` when the server accumulates more than 5 backwards extremities at a given depth for a room.

synapse/handlers/federation.py

@@ -157,7 +157,7 @@ async def _maybe_backfill_inner(
         )
 
         if not oldest_events_with_depth and not insertion_events_to_be_backfilled:
-            logger.debug("Not backfilling as no extremeties found.")
+            logger.info("Not backfilling as no extremeties found.")
             return False
 
         # We only want to paginate if we can actually see the events we'll get,
@@ -240,28 +240,30 @@ async def _maybe_backfill_inner(
             )
             return False
 
-        logger.debug(
-            "room_id: %s, backfill: current_depth: %s, max_depth: %s, extrems: %s",
-            room_id,
-            current_depth,
-            max_depth,
-            sorted_extremeties_tuple,
-        )
-
         # We ignore extremities that have a greater depth than our current depth
         # as:
         #    1. we don't really care about getting events that have happened
-        #       before our current position; and
+        #       after our current position; and
         #    2. we have likely previously tried and failed to backfill from that
         #       extremity, so to avoid getting "stuck" requesting the same
         #       backfill repeatedly we drop those extremities.
         filtered_sorted_extremeties_tuple = [
             t for t in sorted_extremeties_tuple if int(t[1]) <= current_depth
         ]
 
+        logger.debug(
+            "room_id: %s, backfill: current_depth: %s, limit: %s, max_depth: %s, extrems: %s filtered_sorted_extremeties_tuple: %s",
+            room_id,
+            current_depth,
+            limit,
+            max_depth,
+            sorted_extremeties_tuple,
+            filtered_sorted_extremeties_tuple,
+        )
+
         # However, we need to check that the filtered extremities are non-empty.
         # If they are empty then either we can a) bail or b) still attempt to
-        # backill. We opt to try backfilling anyway just in case we do get
+        # backfill. We opt to try backfilling anyway just in case we do get
         # relevant events.
         if filtered_sorted_extremeties_tuple:
             sorted_extremeties_tuple = filtered_sorted_extremeties_tuple
@@ -318,7 +320,7 @@ async def try_backfill(domains: List[str]) -> bool:
             for dom in domains:
                 try:
                     await self._federation_event_handler.backfill(
-                        dom, room_id, limit=100, extremities=extremities
+                        dom, room_id, limit=100, extremities=extremities.keys()
                     )
                     # If this succeeded then we probably already have the
                     # appropriate stuff.
@@ -391,7 +393,7 @@ async def try_backfill(domains: List[str]) -> bool:
             for key, state_dict in states.items()
         }
 
-        for e_id, _ in sorted_extremeties_tuple:
+        for e_id in event_ids:
             likely_extremeties_domains = get_domains_from_state(states[e_id])
 
             success = await try_backfill(

synapse/storage/databases/main/user_directory.py

@@ -383,6 +383,7 @@ async def should_include_local_user_in_dir(self, user: str) -> bool:
         """Certain classes of local user are omitted from the user directory.
         Is this user one of them?
         """
+
         # App service users aren't usually contactable, so exclude them.
         if self.get_if_app_services_interested_in_user(user):
             # TODO we might want to make this configurable for each app service