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The state cache bases its size on the sum of the size of entries. The size of the entry is calculated once on insertion, so it is important that the size of entries does not change. The DictionaryCache modified the entries size, which caused the state cache to incorrectly think it was smaller than it actually was.
145 lines
4.9 KiB
Python
145 lines
4.9 KiB
Python
# -*- coding: utf-8 -*-
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# Copyright 2015, 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.lrucache import LruCache
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from collections import namedtuple
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from . import register_cache
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import threading
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import logging
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logger = logging.getLogger(__name__)
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class DictionaryEntry(namedtuple("DictionaryEntry", ("full", "known_absent", "value"))):
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"""Returned when getting an entry from the cache
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Attributes:
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full (bool): Whether the cache has the full or dict or just some keys.
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If not full then not all requested keys will necessarily be present
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in `value`
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known_absent (set): Keys that were looked up in the dict and were not
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there.
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value (dict): The full or partial dict value
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"""
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def __len__(self):
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return len(self.value)
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class DictionaryCache(object):
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"""Caches key -> dictionary lookups, supporting caching partial dicts, i.e.
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fetching a subset of dictionary keys for a particular key.
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"""
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def __init__(self, name, max_entries=1000):
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self.cache = LruCache(max_size=max_entries, size_callback=len)
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self.name = name
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self.sequence = 0
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self.thread = None
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# caches_by_name[name] = self.cache
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class Sentinel(object):
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__slots__ = []
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self.sentinel = Sentinel()
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self.metrics = register_cache(name, self.cache)
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def check_thread(self):
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expected_thread = self.thread
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if expected_thread is None:
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self.thread = threading.current_thread()
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else:
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if expected_thread is not threading.current_thread():
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raise ValueError(
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"Cache objects can only be accessed from the main thread"
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)
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def get(self, key, dict_keys=None):
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"""Fetch an entry out of the cache
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Args:
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key
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dict_key(list): If given a set of keys then return only those keys
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that exist in the cache.
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Returns:
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DictionaryEntry
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"""
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entry = self.cache.get(key, self.sentinel)
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if entry is not self.sentinel:
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self.metrics.inc_hits()
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if dict_keys is None:
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return DictionaryEntry(entry.full, entry.known_absent, dict(entry.value))
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else:
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return DictionaryEntry(entry.full, entry.known_absent, {
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k: entry.value[k]
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for k in dict_keys
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if k in entry.value
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})
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self.metrics.inc_misses()
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return DictionaryEntry(False, set(), {})
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def invalidate(self, key):
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self.check_thread()
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# Increment the sequence number so that any SELECT statements that
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# raced with the INSERT don't update the cache (SYN-369)
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self.sequence += 1
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self.cache.pop(key, None)
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def invalidate_all(self):
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self.check_thread()
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self.sequence += 1
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self.cache.clear()
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def update(self, sequence, key, value, full=False, known_absent=None):
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"""Updates the entry in the cache
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Args:
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sequence
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key
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value (dict): The value to update the cache with.
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full (bool): Whether the given value is the full dict, or just a
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partial subset there of. If not full then any existing entries
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for the key will be updated.
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known_absent (set): Set of keys that we know don't exist in the full
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dict.
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"""
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self.check_thread()
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if self.sequence == sequence:
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# Only update the cache if the caches sequence number matches the
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# number that the cache had before the SELECT was started (SYN-369)
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if known_absent is None:
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known_absent = set()
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if full:
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self._insert(key, value, known_absent)
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else:
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self._update_or_insert(key, value, known_absent)
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def _update_or_insert(self, key, value, known_absent):
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# We pop and reinsert as we need to tell the cache the size may have
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# changed
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entry = self.cache.pop(key, DictionaryEntry(False, set(), {}))
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entry.value.update(value)
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entry.known_absent.update(known_absent)
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self.cache[key] = entry
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def _insert(self, key, value, known_absent):
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self.cache[key] = DictionaryEntry(True, known_absent, value)
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