Update synapse/storage/databases/main/state.py

Co-authored-by: Richard van der Hoff <1389908+richvdh@users.noreply.github.com>

synapse/storage/databases/main/state.py

@@ -182,11 +182,11 @@ def get_metadata_for_events_txn(
 
         result_map: Dict[str, EventMetadata] = {}
         for batch_ids in batch_iter(event_ids, 1000):
-            result_map = await self.db_pool.runInteraction(
+            result_map.update(await self.db_pool.runInteraction(
                 "get_metadata_for_events",
                 get_metadata_for_events_txn,
                 batch_ids=batch_ids,
-            )
+            ))
 
         return result_map