synapse-product/synapse/util/caches/stream_change_cache.py

# -*- 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

from sortedcontainers import SortedDict

from synapse.util import caches

logger = logging.getLogger(__name__)


class StreamChangeCache(object):
    """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, current_stream_pos, max_size=10000, prefilled_cache=None):
        self._max_size = int(max_size * caches.CACHE_SIZE_FACTOR)
        self._entity_to_key = {}
        self._cache = SortedDict()
        self._earliest_known_stream_pos = current_stream_pos
        self.name = name
        self.metrics = caches.register_cache("cache", self.name, self._cache)

        if prefilled_cache:
            for entity, stream_pos in prefilled_cache.items():
                self.entity_has_changed(entity, stream_pos)

    def has_entity_changed(self, entity, stream_pos):
        """Returns True if the entity may have been updated since stream_pos
        """
        assert type(stream_pos) is int or type(stream_pos) is long

        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, stream_pos):
        """
        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.
        """
        assert type(stream_pos) is int

        if stream_pos >= self._earliest_known_stream_pos:
            changed_entities = {
                self._cache[k] for k in self._cache.islice(
                    start=self._cache.bisect_right(stream_pos),
                )
            }

            # we need to include entities which we don't know about, as well as
            # those which are known to have changed since the stream pos.
            result = {
                e for e in entities
                if e in changed_entities or e not in self._entity_to_key
            }

            self.metrics.inc_hits()
        else:
            result = set(entities)
            self.metrics.inc_misses()

        return result

    def has_any_entity_changed(self, stream_pos):
        """Returns if any entity has changed
        """
        assert type(stream_pos) is int

        if not self._cache:
            # If we have no cache, 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):
        """Returns all entites that have had new things since the given
        position. If the position is too old it will return None.
        """
        assert type(stream_pos) is int

        if stream_pos >= self._earliest_known_stream_pos:
            return [self._cache[k] for k in self._cache.islice(
                start=self._cache.bisect_right(stream_pos))]
        else:
            return None

    def entity_has_changed(self, entity, stream_pos):
        """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:
            old_pos = self._entity_to_key.get(entity, None)
            if old_pos is not None:
                stream_pos = max(stream_pos, old_pos)
                self._cache.pop(old_pos, None)
            self._cache[stream_pos] = entity
            self._entity_to_key[entity] = stream_pos

            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,
                )
                self._entity_to_key.pop(r, None)

    def get_max_pos_of_last_change(self, entity):
        """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)