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Prioritize outbound to-device over device list updates (#13922)
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Otherwise device list changes for large accounts can temporarily delay to-device messages.
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erikjohnston authored Sep 27, 2022
1 parent ac1b0d0 commit 299b00d
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1 change: 1 addition & 0 deletions changelog.d/13922.bugfix
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Fix long-standing bug where device updates could cause delays sending out to-device messages over federation.
29 changes: 16 additions & 13 deletions synapse/federation/sender/per_destination_queue.py
Original file line number Diff line number Diff line change
Expand Up @@ -646,29 +646,32 @@ async def __aenter__(self) -> Tuple[List[EventBase], List[Edu]]:

# We start by fetching device related EDUs, i.e device updates and to
# device messages. We have to keep 2 free slots for presence and rr_edus.
limit = MAX_EDUS_PER_TRANSACTION - 2

device_update_edus, dev_list_id = await self.queue._get_device_update_edus(
limit
)

if device_update_edus:
self._device_list_id = dev_list_id
else:
self.queue._last_device_list_stream_id = dev_list_id

limit -= len(device_update_edus)
device_edu_limit = MAX_EDUS_PER_TRANSACTION - 2

# We prioritize to-device messages so that existing encryption channels
# work. We also keep a few slots spare (by reducing the limit) so that
# we can still trickle out some device list updates.
(
to_device_edus,
device_stream_id,
) = await self.queue._get_to_device_message_edus(limit)
) = await self.queue._get_to_device_message_edus(device_edu_limit - 10)

if to_device_edus:
self._device_stream_id = device_stream_id
else:
self.queue._last_device_stream_id = device_stream_id

device_edu_limit -= len(to_device_edus)

device_update_edus, dev_list_id = await self.queue._get_device_update_edus(
device_edu_limit
)

if device_update_edus:
self._device_list_id = dev_list_id
else:
self.queue._last_device_list_stream_id = dev_list_id

pending_edus = device_update_edus + to_device_edus

# Now add the read receipt EDU.
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