diff options
| -rw-r--r-- | changelog.d/8349.bugfix | 1 | ||||
| -rw-r--r-- | synapse/handlers/federation.py | 65 | ||||
| -rw-r--r-- | synapse/handlers/pagination.py | 8 | ||||
| -rw-r--r-- | synapse/storage/databases/main/stream.py | 13 |
4 files changed, 67 insertions, 20 deletions
diff --git a/changelog.d/8349.bugfix b/changelog.d/8349.bugfix new file mode 100644 index 0000000000..cf2f531b14 --- /dev/null +++ b/changelog.d/8349.bugfix @@ -0,0 +1 @@ +Fix a longstanding bug where back pagination over federation could get stuck if it failed to handle a received event. diff --git a/synapse/handlers/federation.py b/synapse/handlers/federation.py index 43f2986f89..014dab2940 100644 --- a/synapse/handlers/federation.py +++ b/synapse/handlers/federation.py @@ -943,15 +943,26 @@ class FederationHandler(BaseHandler): return events - async def maybe_backfill(self, room_id, current_depth): + async def maybe_backfill( + self, room_id: str, current_depth: int, limit: int + ) -> bool: """Checks the database to see if we should backfill before paginating, and if so do. + + Args: + room_id + current_depth: The depth from which we're paginating from. This is + used to decide if we should backfill and what extremities to + use. + limit: The number of events that the pagination request will + return. This is used as part of the heuristic to decide if we + should back paginate. """ extremities = await self.store.get_oldest_events_with_depth_in_room(room_id) if not extremities: logger.debug("Not backfilling as no extremeties found.") - return + return False # We only want to paginate if we can actually see the events we'll get, # as otherwise we'll just spend a lot of resources to get redacted @@ -1004,16 +1015,54 @@ class FederationHandler(BaseHandler): sorted_extremeties_tuple = sorted(extremities.items(), key=lambda e: -int(e[1])) max_depth = sorted_extremeties_tuple[0][1] + # If we're approaching an extremity we trigger a backfill, otherwise we + # no-op. + # + # We chose twice the limit here as then clients paginating backwards + # will send pagination requests that trigger backfill at least twice + # using the most recent extremity before it gets removed (see below). We + # chose more than one times the limit in case of failure, but choosing a + # much larger factor will result in triggering a backfill request much + # earlier than necessary. + if current_depth - 2 * limit > max_depth: + logger.debug( + "Not backfilling as we don't need to. %d < %d - 2 * %d", + max_depth, + current_depth, + limit, + ) + return False + + logger.debug( + "room_id: %s, backfill: current_depth: %s, max_depth: %s, extrems: %s", + room_id, + current_depth, + max_depth, + sorted_extremeties_tuple, + ) + + # We ignore extremities that have a greater depth than our current depth + # as: + # 1. we don't really care about getting events that have happened + # before our current position; and + # 2. we have likely previously tried and failed to backfill from that + # extremity, so to avoid getting "stuck" requesting the same + # backfill repeatedly we drop those extremities. + filtered_sorted_extremeties_tuple = [ + t for t in sorted_extremeties_tuple if int(t[1]) <= current_depth + ] + + # However, we need to check that the filtered extremities are non-empty. + # If they are empty then either we can a) bail or b) still attempt to + # backill. We opt to try backfilling anyway just in case we do get + # relevant events. + if filtered_sorted_extremeties_tuple: + sorted_extremeties_tuple = filtered_sorted_extremeties_tuple + # We don't want to specify too many extremities as it causes the backfill # request URI to be too long. extremities = dict(sorted_extremeties_tuple[:5]) - if current_depth > max_depth: - logger.debug( - "Not backfilling as we don't need to. %d < %d", max_depth, current_depth - ) - return - # Now we need to decide which hosts to hit first. # First we try hosts that are already in the room diff --git a/synapse/handlers/pagination.py b/synapse/handlers/pagination.py index 34ed0e2921..6067585f9b 100644 --- a/synapse/handlers/pagination.py +++ b/synapse/handlers/pagination.py @@ -362,9 +362,9 @@ class PaginationHandler: # if we're going backwards, we might need to backfill. This # requires that we have a topo token. if room_token.topological: - max_topo = room_token.topological + curr_topo = room_token.topological else: - max_topo = await self.store.get_max_topological_token( + curr_topo = await self.store.get_current_topological_token( room_id, room_token.stream ) @@ -380,11 +380,11 @@ class PaginationHandler: leave_token = await self.store.get_topological_token_for_event( member_event_id ) - if RoomStreamToken.parse(leave_token).topological < max_topo: + if RoomStreamToken.parse(leave_token).topological < curr_topo: source_config.from_key = str(leave_token) await self.hs.get_handlers().federation_handler.maybe_backfill( - room_id, max_topo + room_id, curr_topo, limit=source_config.limit, ) events, next_key = await self.store.paginate_room_events( diff --git a/synapse/storage/databases/main/stream.py b/synapse/storage/databases/main/stream.py index be6df8a6d1..db20a3db30 100644 --- a/synapse/storage/databases/main/stream.py +++ b/synapse/storage/databases/main/stream.py @@ -648,23 +648,20 @@ class StreamWorkerStore(EventsWorkerStore, SQLBaseStore): ) return "t%d-%d" % (row["topological_ordering"], row["stream_ordering"]) - async def get_max_topological_token(self, room_id: str, stream_key: int) -> int: - """Get the max topological token in a room before the given stream + async def get_current_topological_token(self, room_id: str, stream_key: int) -> int: + """Gets the topological token in a room after or at the given stream ordering. Args: room_id stream_key - - Returns: - The maximum topological token. """ sql = ( - "SELECT coalesce(max(topological_ordering), 0) FROM events" - " WHERE room_id = ? AND stream_ordering < ?" + "SELECT coalesce(MIN(topological_ordering), 0) FROM events" + " WHERE room_id = ? AND stream_ordering >= ?" ) row = await self.db_pool.execute( - "get_max_topological_token", None, sql, room_id, stream_key + "get_current_topological_token", None, sql, room_id, stream_key ) return row[0][0] if row else 0 |