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Speed up fetching device lists changes in sync.

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Currently we copy `users_who_share_room` needlessly about three times,
which is expensive when the set is large (which it can easily be).
This commit is contained in:
Erik Johnston 2020-05-05 17:07:59 +01:00
parent b2dba06079
commit f9073893af
3 changed files with 24 additions and 9 deletions
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19
synapse/util/caches/stream_change_cache.py
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@ -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)