Handle remote receipts better

synapse/storage/databases/main/event_push_actions.py

@@ -865,6 +865,16 @@ def _handle_new_receipts_for_notifs_txn(self, txn: LoggingTransaction) -> bool:
         rows = txn.fetchall()
 
         if not rows:
+            # We always update `event_push_summary_last_receipt_stream_id` to
+            # ensure that we don't rescan the same receipts for remote users.
+            #
+            # This requires repeatable read to be safe.
+            txn.execute(
+                """
+                UPDATE event_push_summary_last_receipt_stream_id
+                SET stream_id = (SELECT COALESCE(MAX(stream_id), 0) FROM receipts_linearized)
+                """
+            )
             return True
 
         for _, room_id, user_id, stream_ordering in rows:
@@ -906,13 +916,15 @@ def _handle_new_receipts_for_notifs_txn(self, txn: LoggingTransaction) -> bool:
                 },
             )
 
-        last_stream_id = rows[-1][0]
-
-        self.db_pool.simple_update_one_txn(
-            txn,
-            table="event_push_summary_last_receipt_stream_id",
-            keyvalues={},
-            updatevalues={"stream_id": last_stream_id},
+        # We always update `event_push_summary_last_receipt_stream_id` to
+        # ensure that we don't rescan the same receipts for remote users.
+        #
+        # This requires repeatable read to be safe.
+        txn.execute(
+            """
+            UPDATE event_push_summary_last_receipt_stream_id
+            SET stream_id = (SELECT COALESCE(MAX(stream_id), 0) FROM receipts_linearized)
+            """
         )
 
         return len(rows) < limit