diff --git a/synapse/util/caches/stream_change_cache.py b/synapse/util/caches/stream_change_cache.py
index 38dc3f501e..e54f80d76e 100644
--- a/synapse/util/caches/stream_change_cache.py
+++ b/synapse/util/caches/stream_change_cache.py
@@ -14,12 +14,13 @@
# limitations under the License.
import logging
-from typing import Dict, Iterable, List, Mapping, Optional, Set
+from typing import Dict, FrozenSet, List, Mapping, Optional, Set, Union
from six import integer_types
from sortedcontainers import SortedDict
+from synapse.types import Collection
from synapse.util import caches
logger = logging.getLogger(__name__)
@@ -85,8 +86,8 @@ class StreamChangeCache:
return False
def get_entities_changed(
- self, entities: Iterable[EntityType], stream_pos: int
- ) -> Set[EntityType]:
+ self, entities: Collection[EntityType], stream_pos: int
+ ) -> Union[Set[EntityType], FrozenSet[EntityType]]:
"""
Returns subset of entities that have had new things since the given
position. Entities unknown to the cache will be returned. If the
@@ -94,7 +95,17 @@ class StreamChangeCache:
"""
changed_entities = self.get_all_entities_changed(stream_pos)
if changed_entities is not None:
- result = set(changed_entities).intersection(entities)
+ # We now do an intersection, trying to do so in the most efficient
+ # way possible (some of these sets are *large*). First check in the
+ # given iterable is already set that we can reuse, otherwise we
+ # create a set of the *smallest* of the two iterables and call
+ # `intersection(..)` on it (this can be twice as fast as the reverse).
+ if isinstance(entities, (set, frozenset)):
+ result = entities.intersection(changed_entities)
+ elif len(changed_entities) < len(entities):
+ result = set(changed_entities).intersection(entities)
+ else:
+ result = set(entities).intersection(changed_entities)
self.metrics.inc_hits()
else:
result = set(entities)
|
