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Sliding Sync: bugfix: ensure we can sync with SSS even with missing rooms #17727

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merged 3 commits into from
Sep 18, 2024
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Sliding Sync: bugfix: ensure we can sync with SSS even with missing rooms #17727

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10b00a2
bugfix: ensure we can sync with SSS even with missing rooms
kegsay Sep 18, 2024
dfd119e
Changelog
kegsay Sep 18, 2024
ca44607
Correct type annotation to account for the cache
kegsay Sep 18, 2024
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1 change: 1 addition & 0 deletions changelog.d/17727.bugfix
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Original file line number Diff line number Diff line change
@@ -0,0 +1 @@
Fix a bug in SSS which could prevent /sync from working for certain user accounts.
6 changes: 5 additions & 1 deletion synapse/storage/databases/main/stream.py
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Expand Up @@ -1469,6 +1469,10 @@ async def bulk_get_last_event_pos_in_room_before_stream_ordering(
recheck_rooms: Set[str] = set()
min_token = end_token.stream
for room_id, stream in uncapped_results.items():
if stream is None:
# Despite the function not directly setting None, the cache can!
# See: https://github.com/element-hq/synapse/issues/17726
continue
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Is continuing the right thing to do here?
Or should this fall into the else case below for further processing?

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I'm following the same semantics as if the room was not in uncapped_results at all, which seems to just ignore the room entirely.

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Yeah that makes sense to me. (This is my first time reading through all this code & it seems to jump around / duplicate itself in places which was a little confusing)

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The caller of this function seems to expect an entry for each room ID?

synapse/synapse/handlers/sliding_sync/room_lists.py

Lines 1909 to 1928 in af998e6

joined_room_positions = (
await self.store.bulk_get_last_event_pos_in_room_before_stream_ordering(
[
room_id
for room_id, room_for_user in sync_room_map.items()
if room_for_user.membership == Membership.JOIN
],
to_token.room_key,
)
)
last_activity_in_room_map.update(joined_room_positions)
return sorted(
sync_room_map.values(),
# Sort by the last activity (stream_ordering) in the room
key=lambda room_info: last_activity_in_room_map[room_info.room_id],
# We want descending order
reverse=True,
)

It looks to me that things have gotten a bit confused here around what to do if a bump stamp can't be found, as we are probably assuming we can always find a bump stamp?

I guess the right thing to do is actually handle missing bump stamps at the call site (on top of this change)

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Looks like this was due to room with an unknown room version.

Have fixed and added regression test in #17733

if stream <= min_token:
results[room_id] = stream
else:
Expand All @@ -1495,7 +1499,7 @@ async def _get_max_event_pos(self, room_id: str) -> int:
@cachedList(cached_method_name="_get_max_event_pos", list_name="room_ids")
async def _bulk_get_max_event_pos(
self, room_ids: StrCollection
) -> Mapping[str, int]:
) -> Mapping[str, Optional[int]]:
"""Fetch the max position of a persisted event in the room."""

# We need to be careful not to return positions ahead of the current
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