1 files changed, 17 insertions, 2 deletions
diff --git a/synapse/app/generic_worker.py b/synapse/app/generic_worker.py
index 5afe52f8d4..28ebf67455 100644
--- a/synapse/app/generic_worker.py
+++ b/synapse/app/generic_worker.py
@@ -863,9 +863,24 @@ class FederationSenderHandler(object):
         a FEDERATION_ACK back to the master, and stores the token that we have processed
          in `federation_stream_position` so that we can restart where we left off.
         """
-        try:
-            self.federation_position = token
+        self.federation_position = token
+
+        # We save and send the ACK to master asynchronously, so we don't block
+        # processing on persistence. We don't need to do this operation for
+        # every single RDATA we receive, we just need to do it periodically.
+
+        if self._fed_position_linearizer.is_queued(None):
+            # There is already a task queued up to save and send the token, so
+            # no need to queue up another task.
+            return
 
+        run_as_background_process("_save_and_send_ack", self._save_and_send_ack)
+
+    async def _save_and_send_ack(self):
+        """Save the current federation position in the database and send an ACK
+        to master with where we're up to.
+        """
+        try:
             # We linearize here to ensure we don't have races updating the token
             #
             # XXX this appears to be redundant, since the ReplicationCommandHandler