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