From 3baf6e1667f0c257f288a28bd542a93c2445fd30 Mon Sep 17 00:00:00 2001 From: Erik Johnston Date: Fri, 21 Sep 2018 16:25:42 +0100 Subject: [PATCH] Fix ExpiringCache.__len__ to be accurate It used to try and produce an estimate, which was sometimes negative. This caused metrics to be sad, so lets always just calculate it from scratch. (This appears to have been a longstanding bug, but one which has been made more of a problem by #3932 and #3933). (This was originally done by Erik as part of #3933. I'm cherry-picking it because really it's a fix in its own right) --- synapse/util/caches/expiringcache.py | 17 +++++++---------- 1 file changed, 7 insertions(+), 10 deletions(-) diff --git a/synapse/util/caches/expiringcache.py b/synapse/util/caches/expiringcache.py index 921a9c5b2..9af4ec4aa 100644 --- a/synapse/util/caches/expiringcache.py +++ b/synapse/util/caches/expiringcache.py @@ -16,6 +16,8 @@ import logging from collections import OrderedDict +from six import itervalues + from synapse.metrics.background_process_metrics import run_as_background_process from synapse.util.caches import register_cache @@ -54,8 +56,6 @@ class ExpiringCache(object): self.iterable = iterable - self._size_estimate = 0 - self.metrics = register_cache("expiring", cache_name, self) if not self._expiry_ms: @@ -74,16 +74,11 @@ class ExpiringCache(object): now = self._clock.time_msec() self._cache[key] = _CacheEntry(now, value) - if self.iterable: - self._size_estimate += len(value) - # Evict if there are now too many items while self._max_len and len(self) > self._max_len: _key, value = self._cache.popitem(last=False) if self.iterable: - removed_len = len(value.value) - self.metrics.inc_evictions(removed_len) - self._size_estimate -= removed_len + self.metrics.inc_evictions(len(value.value)) else: self.metrics.inc_evictions() @@ -134,7 +129,9 @@ class ExpiringCache(object): for k in keys_to_delete: value = self._cache.pop(k) if self.iterable: - self._size_estimate -= len(value.value) + self.metrics.inc_evictions(len(value.value)) + else: + self.metrics.inc_evictions() logger.debug( "[%s] _prune_cache before: %d, after len: %d", @@ -143,7 +140,7 @@ class ExpiringCache(object): def __len__(self): if self.iterable: - return self._size_estimate + return sum(len(entry.value) for entry in itervalues(self._cache)) else: return len(self._cache)