1 files changed, 10 insertions, 16 deletions
diff --git a/synapse/storage/state.py b/synapse/storage/state.py
index 6c32e8f7b3..90ec50bb50 100644
--- a/synapse/storage/state.py
+++ b/synapse/storage/state.py
@@ -264,26 +264,20 @@ class StateStore(SQLBaseStore):
         )
 
     @cachedList(cache=_get_state_group_for_event.cache, list_name="event_ids",
-                num_args=1)
+                num_args=1, inlineCallbacks=True)
     def _get_state_group_for_events(self, event_ids):
         """Returns mapping event_id -> state_group
         """
-        def f(txn):
-            results = {}
-            for event_id in event_ids:
-                results[event_id] = self._simple_select_one_onecol_txn(
-                    txn,
-                    table="event_to_state_groups",
-                    keyvalues={
-                        "event_id": event_id,
-                    },
-                    retcol="state_group",
-                    allow_none=True,
-                )
-
-            return results
+        rows = yield self._simple_select_many_batch(
+            table="event_to_state_groups",
+            column="event_id",
+            iterable=event_ids,
+            keyvalues={},
+            retcols=("event_id", "state_group",),
+            desc="_get_state_group_for_events",
+        )
 
-        return self.runInteraction("_get_state_group_for_events", f)
+        defer.returnValue({row["event_id"]: row["state_group"] for row in rows})
 
     def _get_some_state_from_cache(self, group, types):
         """Checks if group is in cache. See `_get_state_for_groups`