Ensure `(room_id, next_batch_id)` is unique to avoid cross-talk/conflicts between batches (MSC2716) (#10877)

Part of [MSC2716](https://github.com/matrix-org/matrix-doc/pull/2716)

Part of https://github.com/matrix-org/synapse/issues/10737

1 files changed, 4 insertions, 2 deletions

diff --git a/synapse/storage/databases/main/room_batch.py b/synapse/storage/databases/main/room_batch.py

index a383388757..300a563c9e 100644
--- a/synapse/storage/databases/main/room_batch.py
+++ b/synapse/storage/databases/main/room_batch.py
@@ -18,7 +18,9 @@ from synapse.storage._base import SQLBaseStore
 
 
 class RoomBatchStore(SQLBaseStore):
-    async def get_insertion_event_by_batch_id(self, batch_id: str) -> Optional[str]:
+    async def get_insertion_event_by_batch_id(
+        self, room_id: str, batch_id: str
+    ) -> Optional[str]:
         """Retrieve a insertion event ID.
 
         Args:
@@ -30,7 +32,7 @@ class RoomBatchStore(SQLBaseStore):
         """
         return await self.db_pool.simple_select_one_onecol(
             table="insertion_events",
-            keyvalues={"next_batch_id": batch_id},
+            keyvalues={"room_id": room_id, "next_batch_id": batch_id},
             retcol="event_id",
             allow_none=True,
         )