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authorErik Johnston <erik@matrix.org>2018-03-15 15:40:13 +0000
committerErik Johnston <erik@matrix.org>2018-03-15 15:46:54 +0000
commit7c7706f42b56dd61f5eb17679aa12247f7058ed5 (patch)
tree5d45938bcff322833a04e8f072507f7fcdb71b81
parentMerge pull request #3003 from matrix-org/rav/fix_contributing (diff)
downloadsynapse-7c7706f42b56dd61f5eb17679aa12247f7058ed5.tar.xz
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.
-rw-r--r--synapse/util/caches/dictionary_cache.py6
-rw-r--r--synapse/util/caches/lrucache.py8
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)