diff options
| -rw-r--r-- | synapse/storage/data_stores/main/stream.py | 15 |
1 files changed, 13 insertions, 2 deletions
diff --git a/synapse/storage/data_stores/main/stream.py b/synapse/storage/data_stores/main/stream.py index 616ef91d4e..ef0b1426d1 100644 --- a/synapse/storage/data_stores/main/stream.py +++ b/synapse/storage/data_stores/main/stream.py @@ -871,14 +871,25 @@ class StreamWorkerStore(EventsWorkerStore, SQLBaseStore): args.append(int(limit)) + # Using DISTINCT in this SELECT query is quite expensive, because it requires the + # engine to sort on the entire (not limited) result set, i.e. the entire events + # table. We only need to use it when we're filtering on more than two labels, + # because that's the only scenario in which we can possibly to get multiple times + # the same event ID in the results. + if event_filter.labels and len(event_filter.labels) > 1: + select_keywords = "SELECT DISTINCT" + + else: + select_keywords = "SELECT" + sql = ( - "SELECT DISTINCT event_id, topological_ordering, stream_ordering" + "%(select_keywords)s event_id, topological_ordering, stream_ordering" " FROM events" " LEFT JOIN event_labels USING (event_id, room_id, topological_ordering)" " WHERE outlier = ? AND room_id = ? AND %(bounds)s" " ORDER BY topological_ordering %(order)s," " stream_ordering %(order)s LIMIT ?" - ) % {"bounds": bounds, "order": order} + ) % {"select_keywords": select_keywords, "bounds": bounds, "order": order} txn.execute(sql, args) |