diff --git a/changelog.d/13658.bugfix b/changelog.d/13658.bugfix
new file mode 100644
index 0000000000..8740f066bb
--- /dev/null
+++ b/changelog.d/13658.bugfix
@@ -0,0 +1 @@
+Fix MSC3030 `/timestamp_to_event` endpoint to return the correct next event when the events have the same timestamp.
diff --git a/synapse/storage/databases/main/events_worker.py b/synapse/storage/databases/main/events_worker.py
index 8a7cdb024d..9b997c304d 100644
--- a/synapse/storage/databases/main/events_worker.py
+++ b/synapse/storage/databases/main/events_worker.py
@@ -2111,7 +2111,14 @@ class EventsWorkerStore(SQLBaseStore):
AND room_id = ?
/* Make sure event is not rejected */
AND rejections.event_id IS NULL
- ORDER BY origin_server_ts %s
+ /**
+ * First sort by the message timestamp. If the message timestamps are the
+ * same, we want the message that logically comes "next" (before/after
+ * the given timestamp) based on the DAG and its topological order (`depth`).
+ * Finally, we can tie-break based on when it was received on the server
+ * (`stream_ordering`).
+ */
+ ORDER BY origin_server_ts %s, depth %s, stream_ordering %s
LIMIT 1;
"""
@@ -2130,7 +2137,8 @@ class EventsWorkerStore(SQLBaseStore):
order = "ASC"
txn.execute(
- sql_template % (comparison_operator, order), (timestamp, room_id)
+ sql_template % (comparison_operator, order, order, order),
+ (timestamp, room_id),
)
row = txn.fetchone()
if row:
|
