Merge pull request #3544 from matrix-org/erikj/fixup_stream_cache

Fix perf regression in PR #3530

1 files changed, 3 insertions, 1 deletions

diff --git a/synapse/util/caches/stream_change_cache.py b/synapse/util/caches/stream_change_cache.py

index 258655349b..f2bde74dc5 100644
--- a/synapse/util/caches/stream_change_cache.py
+++ b/synapse/util/caches/stream_change_cache.py
@@ -74,12 +74,14 @@ class StreamChangeCache(object):
         assert type(stream_pos) is int
 
         if stream_pos >= self._earliest_known_stream_pos:
-            result = {
+            changed_entities = {
                 self._cache[k] for k in self._cache.islice(
                     start=self._cache.bisect_right(stream_pos),
                 )
             }
 
+            result = changed_entities.intersection(entities)
+
             self.metrics.inc_hits()
         else:
             result = set(entities)