96 lines
3.2 KiB
Python
96 lines
3.2 KiB
Python
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# -*- coding: utf-8 -*-
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# 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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from synapse.util.caches import cache_counter, caches_by_name
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from blist import sorteddict
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import logging
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logger = logging.getLogger(__name__)
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class StreamChangeCache(object):
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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__(self, name, current_stream_pos, max_size=10000):
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self._max_size = max_size
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self._entity_to_key = {}
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self._cache = sorteddict()
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self._earliest_known_stream_pos = current_stream_pos
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self.name = name
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caches_by_name[self.name] = self._cache
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def get_entity_has_changed(self, entity, stream_pos):
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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 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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return True
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if stream_pos < latest_entity_change_pos:
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return True
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return False
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def get_entities_changed(self, entities, stream_pos):
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"""Returns subset of entities that have had new things since the
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given position. If the position is too old it will just return the given list.
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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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keys = self._cache.keys()
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i = keys.bisect_right(stream_pos)
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result = set(
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self._cache[k] for k in keys[i:]
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).intersection(entities)
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cache_counter.inc_hits(self.name)
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else:
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result = entities
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cache_counter.inc_misses(self.name)
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return result
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def entity_has_changed(self, entitiy, stream_pos):
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"""Informs the cache that the entitiy 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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old_pos = self._entity_to_key.get(entitiy, None)
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if old_pos:
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stream_pos = max(stream_pos, old_pos)
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self._cache.pop(old_pos, None)
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self._cache[stream_pos] = entitiy
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while len(self._cache) > self._max_size:
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k, r = self._cache.popitem()
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self._earliest_known_stream_pos = max(k, self._earliest_known_stream_pos)
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self._entity_to_key.pop(r, None)
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