Add some logging for syncing to_device events

Attempt to track down the loss of to_device events
(https://github.com/vector-im/riot-web/issues/2711 etc).

1 files changed, 8 insertions, 4 deletions

diff --git a/synapse/handlers/sync.py b/synapse/handlers/sync.py
index b62773dcbe..c880f61685 100644
--- a/synapse/handlers/sync.py
+++ b/synapse/handlers/sync.py
@@ -576,16 +576,20 @@ class SyncHandler(object):
             # We only delete messages when a new message comes in, but that's
             # fine so long as we delete them at some point.
 
-            logger.debug("Deleting messages up to %d", since_stream_id)
-            yield self.store.delete_messages_for_device(
+            deleted = yield self.store.delete_messages_for_device(
                 user_id, device_id, since_stream_id
             )
+            logger.info("Deleted %d to-device messages up to %d",
+                        deleted, since_stream_id)
 
-            logger.debug("Getting messages up to %d", now_token.to_device_key)
             messages, stream_id = yield self.store.get_new_messages_for_device(
                 user_id, device_id, since_stream_id, now_token.to_device_key
             )
-            logger.debug("Got messages up to %d: %r", stream_id, messages)
+
+            logger.info(
+                "Returning %d to-device messages between %d and %d (current token: %d)",
+                len(messages), since_stream_id, stream_id, now_token.to_device_key
+            )
             sync_result_builder.now_token = now_token.copy_and_replace(
                 "to_device_key", stream_id
             )