From 7c7706f42b56dd61f5eb17679aa12247f7058ed5 Mon Sep 17 00:00:00 2001 From: Erik Johnston Date: Thu, 15 Mar 2018 15:40:13 +0000 Subject: [PATCH 1/2] Fix bug where state cache used lots of memory 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. --- synapse/util/caches/dictionary_cache.py | 6 +++++- synapse/util/caches/lrucache.py | 8 ++++---- 2 files changed, 9 insertions(+), 5 deletions(-) diff --git a/synapse/util/caches/dictionary_cache.py b/synapse/util/caches/dictionary_cache.py index d4105822b3..1709e8b429 100644 --- a/synapse/util/caches/dictionary_cache.py +++ b/synapse/util/caches/dictionary_cache.py @@ -132,9 +132,13 @@ class DictionaryCache(object): self._update_or_insert(key, value, known_absent) def _update_or_insert(self, key, value, known_absent): - entry = self.cache.setdefault(key, DictionaryEntry(False, set(), {})) + # We pop and reinsert as we need to tell the cache the size may have + # changed + + entry = self.cache.pop(key, DictionaryEntry(False, set(), {})) entry.value.update(value) entry.known_absent.update(known_absent) + self.cache[key] = entry def _insert(self, key, value, known_absent): self.cache[key] = DictionaryEntry(True, known_absent, value) diff --git a/synapse/util/caches/lrucache.py b/synapse/util/caches/lrucache.py index f088dd430e..a4bf8fa6ae 100644 --- a/synapse/util/caches/lrucache.py +++ b/synapse/util/caches/lrucache.py @@ -154,14 +154,14 @@ class LruCache(object): def cache_set(key, value, callbacks=[]): node = cache.get(key, None) if node is not None: - if value != node.value: + if node.callbacks and value != node.value: for cb in node.callbacks: cb() node.callbacks.clear() - if size_callback: - cached_cache_len[0] -= size_callback(node.value) - cached_cache_len[0] += size_callback(value) + if size_callback: + cached_cache_len[0] -= size_callback(node.value) + cached_cache_len[0] += size_callback(value) node.callbacks.update(callbacks) From 9a0d783c113ae74c55e409d33219cd77f3662b9f Mon Sep 17 00:00:00 2001 From: Erik Johnston Date: Mon, 19 Mar 2018 11:35:53 +0000 Subject: [PATCH 2/2] Add comments --- synapse/util/caches/lrucache.py | 7 +++++++ 1 file changed, 7 insertions(+) diff --git a/synapse/util/caches/lrucache.py b/synapse/util/caches/lrucache.py index a4bf8fa6ae..1c5a982094 100644 --- a/synapse/util/caches/lrucache.py +++ b/synapse/util/caches/lrucache.py @@ -154,11 +154,18 @@ class LruCache(object): def cache_set(key, value, callbacks=[]): node = cache.get(key, None) if node is not None: + # We sometimes store large objects, e.g. dicts, which cause + # the inequality check to take a long time. So let's only do + # the check if we have some callbacks to call. if node.callbacks and value != node.value: for cb in node.callbacks: cb() node.callbacks.clear() + # We don't bother to protect this by value != node.value as + # generally size_callback will be cheap compared with equality + # checks. (For example, taking the size of two dicts is quicker + # than comparing them for equality.) if size_callback: cached_cache_len[0] -= size_callback(node.value) cached_cache_len[0] += size_callback(value)