Skip processing stats for broken rooms. (#14873)

* Skip processing stats for broken rooms.

* Newsfragment

* Use a custom exception.

2 files changed, 17 insertions, 2 deletions

diff --git a/synapse/storage/databases/main/events_worker.py b/synapse/storage/databases/main/events_worker.py
index 24127d0364..f42af34a2f 100644
--- a/synapse/storage/databases/main/events_worker.py
+++ b/synapse/storage/databases/main/events_worker.py
@@ -110,6 +110,10 @@ event_fetch_ongoing_gauge = Gauge(
 )
 
 
+class InvalidEventError(Exception):
+    """The event retrieved from the database is invalid and cannot be used."""
+
+
 @attr.s(slots=True, auto_attribs=True)
 class EventCacheEntry:
     event: EventBase
@@ -1310,7 +1314,7 @@ class EventsWorkerStore(SQLBaseStore):
                 # invites, so just accept it for all membership events.
                 #
                 if d["type"] != EventTypes.Member:
-                    raise Exception(
+                    raise InvalidEventError(
                         "Room %s for event %s is unknown" % (d["room_id"], event_id)
                     )
 
diff --git a/synapse/storage/databases/main/stats.py b/synapse/storage/databases/main/stats.py
index 356d4ca788..0c1cbd540d 100644
--- a/synapse/storage/databases/main/stats.py
+++ b/synapse/storage/databases/main/stats.py
@@ -29,6 +29,7 @@ from synapse.storage.database import (
     LoggingDatabaseConnection,
     LoggingTransaction,
 )
+from synapse.storage.databases.main.events_worker import InvalidEventError
 from synapse.storage.databases.main.state_deltas import StateDeltasStore
 from synapse.types import JsonDict
 from synapse.util.caches.descriptors import cached
@@ -554,7 +555,17 @@ class StatsStore(StateDeltasStore):
             "get_initial_state_for_room", _fetch_current_state_stats
         )
 
-        state_event_map = await self.get_events(event_ids, get_prev_content=False)  # type: ignore[attr-defined]
+        try:
+            state_event_map = await self.get_events(event_ids, get_prev_content=False)  # type: ignore[attr-defined]
+        except InvalidEventError as e:
+            # If an exception occurs fetching events then the room is broken;
+            # skip process it to avoid being stuck on a room.
+            logger.warning(
+                "Failed to fetch events for room %s, skipping stats calculation: %r.",
+                room_id,
+                e,
+            )
+            return
 
         room_state: Dict[str, Union[None, bool, str]] = {
             "join_rules": None,