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- # -*- coding: utf-8 -*-
- # Copyright 2016 OpenMarket Ltd
- #
- # Licensed under the Apache License, Version 2.0 (the "License");
- # you may not use this file except in compliance with the License.
- # You may obtain a copy of the License at
- #
- # http://www.apache.org/licenses/LICENSE-2.0
- #
- # Unless required by applicable law or agreed to in writing, software
- # distributed under the License is distributed on an "AS IS" BASIS,
- # WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
- # See the License for the specific language governing permissions and
- # limitations under the License.
- import logging
- import math
- from typing import Dict, FrozenSet, List, Mapping, Optional, Set, Union
- from sortedcontainers import SortedDict
- from synapse.types import Collection
- from synapse.util import caches
- logger = logging.getLogger(__name__)
- # for now, assume all entities in the cache are strings
- EntityType = str
- class StreamChangeCache:
- """Keeps track of the stream positions of the latest change in a set of entities.
- Typically the entity will be a room or user id.
- Given a list of entities and a stream position, it will give a subset of
- entities that may have changed since that position. If position key is too
- old then the cache will simply return all given entities.
- """
- def __init__(
- self,
- name: str,
- current_stream_pos: int,
- max_size=10000,
- prefilled_cache: Optional[Mapping[EntityType, int]] = None,
- ):
- self._original_max_size = max_size
- self._max_size = math.floor(max_size)
- self._entity_to_key = {} # type: Dict[EntityType, int]
- # map from stream id to the a set of entities which changed at that stream id.
- self._cache = SortedDict() # type: SortedDict[int, Set[EntityType]]
- # the earliest stream_pos for which we can reliably answer
- # get_all_entities_changed. In other words, one less than the earliest
- # stream_pos for which we know _cache is valid.
- #
- self._earliest_known_stream_pos = current_stream_pos
- self.name = name
- self.metrics = caches.register_cache(
- "cache", self.name, self._cache, resize_callback=self.set_cache_factor
- )
- if prefilled_cache:
- for entity, stream_pos in prefilled_cache.items():
- self.entity_has_changed(entity, stream_pos)
- def set_cache_factor(self, factor: float) -> bool:
- """
- Set the cache factor for this individual cache.
- This will trigger a resize if it changes, which may require evicting
- items from the cache.
- Returns:
- bool: Whether the cache changed size or not.
- """
- new_size = math.floor(self._original_max_size * factor)
- if new_size != self._max_size:
- self.max_size = new_size
- self._evict()
- return True
- return False
- def has_entity_changed(self, entity: EntityType, stream_pos: int) -> bool:
- """Returns True if the entity may have been updated since stream_pos
- """
- assert isinstance(stream_pos, int)
- if stream_pos < self._earliest_known_stream_pos:
- self.metrics.inc_misses()
- return True
- latest_entity_change_pos = self._entity_to_key.get(entity, None)
- if latest_entity_change_pos is None:
- self.metrics.inc_hits()
- return False
- if stream_pos < latest_entity_change_pos:
- self.metrics.inc_misses()
- return True
- self.metrics.inc_hits()
- return False
- def get_entities_changed(
- 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
- position is too old it will just return the given list.
- """
- changed_entities = self.get_all_entities_changed(stream_pos)
- if changed_entities is not None:
- # 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)
- self.metrics.inc_misses()
- return result
- def has_any_entity_changed(self, stream_pos: int) -> bool:
- """Returns if any entity has changed
- """
- assert type(stream_pos) is int
- if not self._cache:
- # If the cache is empty, nothing can have changed.
- return False
- if stream_pos >= self._earliest_known_stream_pos:
- self.metrics.inc_hits()
- return self._cache.bisect_right(stream_pos) < len(self._cache)
- else:
- self.metrics.inc_misses()
- return True
- def get_all_entities_changed(self, stream_pos: int) -> Optional[List[EntityType]]:
- """Returns all entities that have had new things since the given
- position. If the position is too old it will return None.
- Returns the entities in the order that they were changed.
- """
- assert type(stream_pos) is int
- if stream_pos < self._earliest_known_stream_pos:
- return None
- changed_entities = [] # type: List[EntityType]
- for k in self._cache.islice(start=self._cache.bisect_right(stream_pos)):
- changed_entities.extend(self._cache[k])
- return changed_entities
- def entity_has_changed(self, entity: EntityType, stream_pos: int) -> None:
- """Informs the cache that the entity has been changed at the given
- position.
- """
- assert type(stream_pos) is int
- if stream_pos <= self._earliest_known_stream_pos:
- return
- old_pos = self._entity_to_key.get(entity, None)
- if old_pos is not None:
- if old_pos >= stream_pos:
- # nothing to do
- return
- e = self._cache[old_pos]
- e.remove(entity)
- if not e:
- # cache at this point is now empty
- del self._cache[old_pos]
- e1 = self._cache.get(stream_pos)
- if e1 is None:
- e1 = self._cache[stream_pos] = set()
- e1.add(entity)
- self._entity_to_key[entity] = stream_pos
- self._evict()
- # if the cache is too big, remove entries
- while len(self._cache) > self._max_size:
- k, r = self._cache.popitem(0)
- self._earliest_known_stream_pos = max(k, self._earliest_known_stream_pos)
- for entity in r:
- del self._entity_to_key[entity]
- def _evict(self):
- while len(self._cache) > self._max_size:
- k, r = self._cache.popitem(0)
- self._earliest_known_stream_pos = max(k, self._earliest_known_stream_pos)
- for entity in r:
- self._entity_to_key.pop(entity, None)
- def get_max_pos_of_last_change(self, entity: EntityType) -> int:
- """Returns an upper bound of the stream id of the last change to an
- entity.
- """
- return self._entity_to_key.get(entity, self._earliest_known_stream_pos)
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