Merge pull request #1815 from matrix-org/erikj/iter_cache_size

Optionally measure size of cache by sum of length of values

synapse/state.py

@@ -41,7 +41,7 @@ KeyStateTuple = namedtuple("KeyStateTuple", ("context", "type", "state_key"))
 CACHE_SIZE_FACTOR = float(os.environ.get("SYNAPSE_CACHE_FACTOR", 0.1))
 
 
-SIZE_OF_CACHE = int(1000 * CACHE_SIZE_FACTOR)
+SIZE_OF_CACHE = int(100000 * CACHE_SIZE_FACTOR)
 EVICTION_TIMEOUT_SECONDS = 60 * 60
 
 
@@ -77,6 +77,9 @@ class _StateCacheEntry(object):
         else:
             self.state_id = _gen_state_id()
 
+    def __len__(self):
+        return len(self.state)
+
 
 class StateHandler(object):
     """ Responsible for doing state conflict resolution.
@@ -99,6 +102,7 @@ class StateHandler(object):
             clock=self.clock,
             max_len=SIZE_OF_CACHE,
             expiry_ms=EVICTION_TIMEOUT_SECONDS * 1000,
+            iterable=True,
             reset_expiry_on_get=True,
         )
 

synapse/storage/_base.py

@@ -169,7 +169,7 @@ class SQLBaseStore(object):
                                       max_entries=hs.config.event_cache_size)
 
         self._state_group_cache = DictionaryCache(
-            "*stateGroupCache*", 2000 * CACHE_SIZE_FACTOR
+            "*stateGroupCache*", 100000 * CACHE_SIZE_FACTOR
         )
 
         self._event_fetch_lock = threading.Condition()

synapse/storage/roommember.py

@@ -390,7 +390,8 @@ class RoomMemberStore(SQLBaseStore):
             room_id, state_group, state_ids,
         )
 
-    @cachedInlineCallbacks(num_args=2, cache_context=True)
+    @cachedInlineCallbacks(num_args=2, cache_context=True, iterable=True,
+                           max_entries=100000)
     def _get_joined_users_from_context(self, room_id, state_group, current_state_ids,
                                        cache_context, event=None):
         # We don't use `state_group`, it's there so that we can cache based

synapse/storage/state.py

@@ -284,7 +284,7 @@ class StateStore(SQLBaseStore):
             return [r[0] for r in results]
         return self.runInteraction("get_current_state_for_key", f)
 
-    @cached(num_args=2, max_entries=1000)
+    @cached(num_args=2, max_entries=100000, iterable=True)
     def _get_state_group_from_group(self, group, types):
         raise NotImplementedError()
 

synapse/util/caches/descriptors.py

@@ -17,7 +17,7 @@ import logging
 from synapse.util.async import ObservableDeferred
 from synapse.util import unwrapFirstError
 from synapse.util.caches.lrucache import LruCache
-from synapse.util.caches.treecache import TreeCache
+from synapse.util.caches.treecache import TreeCache, iterate_tree_cache_entry
 from synapse.util.logcontext import (
     PreserveLoggingContext, preserve_context_over_deferred, preserve_context_over_fn
 )
@@ -42,6 +42,25 @@ _CacheSentinel = object()
 CACHE_SIZE_FACTOR = float(os.environ.get("SYNAPSE_CACHE_FACTOR", 0.1))
 
 
+class CacheEntry(object):
+    __slots__ = [
+        "deferred", "sequence", "callbacks", "invalidated"
+    ]
+
+    def __init__(self, deferred, sequence, callbacks):
+        self.deferred = deferred
+        self.sequence = sequence
+        self.callbacks = set(callbacks)
+        self.invalidated = False
+
+    def invalidate(self):
+        if not self.invalidated:
+            self.invalidated = True
+            for callback in self.callbacks:
+                callback()
+            self.callbacks.clear()
+
+
 class Cache(object):
     __slots__ = (
         "cache",
@@ -51,12 +70,16 @@ class Cache(object):
         "sequence",
         "thread",
         "metrics",
+        "_pending_deferred_cache",
     )
 
-    def __init__(self, name, max_entries=1000, keylen=1, tree=False):
+    def __init__(self, name, max_entries=1000, keylen=1, tree=False, iterable=False):
         cache_type = TreeCache if tree else dict
+        self._pending_deferred_cache = cache_type()
+
         self.cache = LruCache(
-            max_size=max_entries, keylen=keylen, cache_type=cache_type
+            max_size=max_entries, keylen=keylen, cache_type=cache_type,
+            size_callback=(lambda d: len(d.result)) if iterable else None,
         )
 
         self.name = name
@@ -76,7 +99,15 @@ class Cache(object):
                 )
 
     def get(self, key, default=_CacheSentinel, callback=None):
-        val = self.cache.get(key, _CacheSentinel, callback=callback)
+        callbacks = [callback] if callback else []
+        val = self._pending_deferred_cache.get(key, _CacheSentinel)
+        if val is not _CacheSentinel:
+            if val.sequence == self.sequence:
+                val.callbacks.update(callbacks)
+                self.metrics.inc_hits()
+                return val.deferred
+
+        val = self.cache.get(key, _CacheSentinel, callbacks=callbacks)
         if val is not _CacheSentinel:
             self.metrics.inc_hits()
             return val
@@ -88,15 +119,39 @@ class Cache(object):
         else:
             return default
 
-    def update(self, sequence, key, value, callback=None):
+    def set(self, key, value, callback=None):
+        callbacks = [callback] if callback else []
         self.check_thread()
-        if self.sequence == sequence:
+        entry = CacheEntry(
-            # Only update the cache if the caches sequence number matches the
+            deferred=value,
-            # number that the cache had before the SELECT was started (SYN-369)
+            sequence=self.sequence,
-            self.prefill(key, value, callback=callback)
+            callbacks=callbacks,
+        )
+
+        entry.callbacks.update(callbacks)
+
+        existing_entry = self._pending_deferred_cache.pop(key, None)
+        if existing_entry:
+            existing_entry.invalidate()
+
+        self._pending_deferred_cache[key] = entry
+
+        def shuffle(result):
+            if self.sequence == entry.sequence:
+                existing_entry = self._pending_deferred_cache.pop(key, None)
+                if existing_entry is entry:
+                    self.cache.set(key, entry.deferred, entry.callbacks)
+                else:
+                    entry.invalidate()
+            else:
+                entry.invalidate()
+            return result
+
+        entry.deferred.addCallback(shuffle)
 
     def prefill(self, key, value, callback=None):
-        self.cache.set(key, value, callback=callback)
+        callbacks = [callback] if callback else []
+        self.cache.set(key, value, callbacks=callbacks)
 
     def invalidate(self, key):
         self.check_thread()
@@ -108,6 +163,10 @@ class Cache(object):
         # Increment the sequence number so that any SELECT statements that
         # raced with the INSERT don't update the cache (SYN-369)
         self.sequence += 1
+        entry = self._pending_deferred_cache.pop(key, None)
+        if entry:
+            entry.invalidate()
+
         self.cache.pop(key, None)
 
     def invalidate_many(self, key):
@@ -119,6 +178,12 @@ class Cache(object):
         self.sequence += 1
         self.cache.del_multi(key)
 
+        val = self._pending_deferred_cache.pop(key, None)
+        if val is not None:
+            entry_dict, _ = val
+            for entry in iterate_tree_cache_entry(entry_dict):
+                entry.invalidate()
+
     def invalidate_all(self):
         self.check_thread()
         self.sequence += 1
@@ -155,7 +220,7 @@ class CacheDescriptor(object):
 
     """
     def __init__(self, orig, max_entries=1000, num_args=1, tree=False,
-                 inlineCallbacks=False, cache_context=False):
+                 inlineCallbacks=False, cache_context=False, iterable=False):
         max_entries = int(max_entries * CACHE_SIZE_FACTOR)
 
         self.orig = orig
@@ -169,6 +234,8 @@ class CacheDescriptor(object):
         self.num_args = num_args
         self.tree = tree
 
+        self.iterable = iterable
+
         all_args = inspect.getargspec(orig)
         self.arg_names = all_args.args[1:num_args + 1]
 
@@ -203,6 +270,7 @@ class CacheDescriptor(object):
             max_entries=self.max_entries,
             keylen=self.num_args,
             tree=self.tree,
+            iterable=self.iterable,
         )
 
         @functools.wraps(self.orig)
@@ -243,11 +311,6 @@ class CacheDescriptor(object):
 
                 return preserve_context_over_deferred(observer)
             except KeyError:
-                # Get the sequence number of the cache before reading from the
-                # database so that we can tell if the cache is invalidated
-                # while the SELECT is executing (SYN-369)
-                sequence = cache.sequence
-
                 ret = defer.maybeDeferred(
                     preserve_context_over_fn,
                     self.function_to_call,
@@ -261,7 +324,7 @@ class CacheDescriptor(object):
                 ret.addErrback(onErr)
 
                 ret = ObservableDeferred(ret, consumeErrors=True)
-                cache.update(sequence, cache_key, ret, callback=invalidate_callback)
+                cache.set(cache_key, ret, callback=invalidate_callback)
 
                 return preserve_context_over_deferred(ret.observe())
 
@@ -359,7 +422,6 @@ class CacheListDescriptor(object):
                     missing.append(arg)
 
             if missing:
-                sequence = cache.sequence
                 args_to_call = dict(arg_dict)
                 args_to_call[self.list_name] = missing
 
@@ -382,8 +444,8 @@ class CacheListDescriptor(object):
 
                     key = list(keyargs)
                     key[self.list_pos] = arg
-                    cache.update(
+                    cache.set(
-                        sequence, tuple(key), observer,
+                        tuple(key), observer,
                         callback=invalidate_callback
                     )
 
@@ -421,17 +483,20 @@ class _CacheContext(namedtuple("_CacheContext", ("cache", "key"))):
         self.cache.invalidate(self.key)
 
 
-def cached(max_entries=1000, num_args=1, tree=False, cache_context=False):
+def cached(max_entries=1000, num_args=1, tree=False, cache_context=False,
+           iterable=False):
     return lambda orig: CacheDescriptor(
         orig,
         max_entries=max_entries,
         num_args=num_args,
         tree=tree,
         cache_context=cache_context,
+        iterable=iterable,
     )
 
 
-def cachedInlineCallbacks(max_entries=1000, num_args=1, tree=False, cache_context=False):
+def cachedInlineCallbacks(max_entries=1000, num_args=1, tree=False, cache_context=False,
+                          iterable=False):
     return lambda orig: CacheDescriptor(
         orig,
         max_entries=max_entries,
@@ -439,6 +504,7 @@ def cachedInlineCallbacks(max_entries=1000, num_args=1, tree=False, cache_contex
         tree=tree,
         inlineCallbacks=True,
         cache_context=cache_context,
+        iterable=iterable,
     )
 
 

synapse/util/caches/dictionary_cache.py

@@ -23,7 +23,9 @@ import logging
 logger = logging.getLogger(__name__)
 
 
-DictionaryEntry = namedtuple("DictionaryEntry", ("full", "value"))
+class DictionaryEntry(namedtuple("DictionaryEntry", ("full", "value"))):
+    def __len__(self):
+        return len(self.value)
 
 
 class DictionaryCache(object):
@@ -32,7 +34,7 @@ class DictionaryCache(object):
     """
 
     def __init__(self, name, max_entries=1000):
-        self.cache = LruCache(max_size=max_entries)
+        self.cache = LruCache(max_size=max_entries, size_callback=len)
 
         self.name = name
         self.sequence = 0

synapse/util/caches/expiringcache.py

@@ -15,6 +15,7 @@
 
 from synapse.util.caches import register_cache
 
+from collections import OrderedDict
 import logging
 
 
@@ -23,7 +24,7 @@ logger = logging.getLogger(__name__)
 
 class ExpiringCache(object):
     def __init__(self, cache_name, clock, max_len=0, expiry_ms=0,
-                 reset_expiry_on_get=False):
+                 reset_expiry_on_get=False, iterable=False):
         """
         Args:
             cache_name (str): Name of this cache, used for logging.
@@ -36,6 +37,8 @@ class ExpiringCache(object):
                 evicted based on time.
             reset_expiry_on_get (bool): If true, will reset the expiry time for
                 an item on access. Defaults to False.
+            iterable (bool): If true, the size is calculated by summing the
+                sizes of all entries, rather than the number of entries.
 
         """
         self._cache_name = cache_name
@@ -47,9 +50,13 @@ class ExpiringCache(object):
 
         self._reset_expiry_on_get = reset_expiry_on_get
 
-        self._cache = {}
+        self._cache = OrderedDict()
 
-        self.metrics = register_cache(cache_name, self._cache)
+        self.metrics = register_cache(cache_name, self)
+
+        self.iterable = iterable
+
+        self._size_estimate = 0
 
     def start(self):
         if not self._expiry_ms:
@@ -65,15 +72,14 @@ class ExpiringCache(object):
         now = self._clock.time_msec()
         self._cache[key] = _CacheEntry(now, value)
 
-        # Evict if there are now too many items
+        if self.iterable:
-        if self._max_len and len(self._cache.keys()) > self._max_len:
+            self._size_estimate += len(value)
-            sorted_entries = sorted(
-                self._cache.items(),
-                key=lambda item: item[1].time,
-            )
 
-            for k, _ in sorted_entries[self._max_len:]:
+        # Evict if there are now too many items
-                self._cache.pop(k)
+        while self._max_len and len(self) > self._max_len:
+            _key, value = self._cache.popitem(last=False)
+            if self.iterable:
+                self._size_estimate -= len(value.value)
 
     def __getitem__(self, key):
         try:
@@ -99,7 +105,7 @@ class ExpiringCache(object):
             # zero expiry time means don't expire. This should never get called
             # since we have this check in start too.
             return
-        begin_length = len(self._cache)
+        begin_length = len(self)
 
         now = self._clock.time_msec()
 
@@ -110,14 +116,19 @@ class ExpiringCache(object):
                 keys_to_delete.add(key)
 
         for k in keys_to_delete:
-            self._cache.pop(k)
+            value = self._cache.pop(k)
+            if self.iterable:
+                self._size_estimate -= len(value.value)
 
         logger.debug(
             "[%s] _prune_cache before: %d, after len: %d",
-            self._cache_name, begin_length, len(self._cache)
+            self._cache_name, begin_length, len(self)
         )
 
     def __len__(self):
+        if self.iterable:
+            return self._size_estimate
+        else:
             return len(self._cache)
 
 

synapse/util/caches/lrucache.py

@@ -49,7 +49,7 @@ class LruCache(object):
     Can also set callbacks on objects when getting/setting which are fired
     when that key gets invalidated/evicted.
     """
-    def __init__(self, max_size, keylen=1, cache_type=dict):
+    def __init__(self, max_size, keylen=1, cache_type=dict, size_callback=None):
         cache = cache_type()
         self.cache = cache  # Used for introspection.
         list_root = _Node(None, None, None, None)
@@ -58,6 +58,12 @@ class LruCache(object):
 
         lock = threading.Lock()
 
+        def evict():
+            while cache_len() > max_size:
+                todelete = list_root.prev_node
+                delete_node(todelete)
+                cache.pop(todelete.key, None)
+
         def synchronized(f):
             @wraps(f)
             def inner(*args, **kwargs):
@@ -66,6 +72,16 @@ class LruCache(object):
 
             return inner
 
+        cached_cache_len = [0]
+        if size_callback is not None:
+            def cache_len():
+                return cached_cache_len[0]
+        else:
+            def cache_len():
+                return len(cache)
+
+        self.len = synchronized(cache_len)
+
         def add_node(key, value, callbacks=set()):
             prev_node = list_root
             next_node = prev_node.next_node
@@ -74,6 +90,9 @@ class LruCache(object):
             next_node.prev_node = node
             cache[key] = node
 
+            if size_callback:
+                cached_cache_len[0] += size_callback(node.value)
+
         def move_node_to_front(node):
             prev_node = node.prev_node
             next_node = node.next_node
@@ -92,23 +111,25 @@ class LruCache(object):
             prev_node.next_node = next_node
             next_node.prev_node = prev_node
 
+            if size_callback:
+                cached_cache_len[0] -= size_callback(node.value)
+
             for cb in node.callbacks:
                 cb()
             node.callbacks.clear()
 
         @synchronized
-        def cache_get(key, default=None, callback=None):
+        def cache_get(key, default=None, callbacks=[]):
             node = cache.get(key, None)
             if node is not None:
                 move_node_to_front(node)
-                if callback:
+                node.callbacks.update(callbacks)
-                    node.callbacks.add(callback)
                 return node.value
             else:
                 return default
 
         @synchronized
-        def cache_set(key, value, callback=None):
+        def cache_set(key, value, callbacks=[]):
             node = cache.get(key, None)
             if node is not None:
                 if value != node.value:
@@ -116,21 +137,18 @@ class LruCache(object):
                         cb()
                     node.callbacks.clear()
 
-                if callback:
+                    if size_callback:
-                    node.callbacks.add(callback)
+                        cached_cache_len[0] -= size_callback(node.value)
+                        cached_cache_len[0] += size_callback(value)
+
+                node.callbacks.update(callbacks)
 
                 move_node_to_front(node)
                 node.value = value
             else:
-                if callback:
+                add_node(key, value, set(callbacks))
-                    callbacks = set([callback])
+
-                else:
+            evict()
-                    callbacks = set()
-                add_node(key, value, callbacks)
-                if len(cache) > max_size:
-                    todelete = list_root.prev_node
-                    delete_node(todelete)
-                    cache.pop(todelete.key, None)
 
         @synchronized
         def cache_set_default(key, value):
@@ -139,10 +157,7 @@ class LruCache(object):
                 return node.value
             else:
                 add_node(key, value)
-                if len(cache) > max_size:
+                evict()
-                    todelete = list_root.prev_node
-                    delete_node(todelete)
-                    cache.pop(todelete.key, None)
                 return value
 
         @synchronized
@@ -175,10 +190,6 @@ class LruCache(object):
                     cb()
             cache.clear()
 
-        @synchronized
-        def cache_len():
-            return len(cache)
-
         @synchronized
         def cache_contains(key):
             return key in cache
@@ -190,7 +201,7 @@ class LruCache(object):
         self.pop = cache_pop
         if cache_type is TreeCache:
             self.del_multi = cache_del_multi
-        self.len = cache_len
+        self.len = synchronized(cache_len)
         self.contains = cache_contains
         self.clear = cache_clear
 

synapse/util/caches/treecache.py

@@ -65,12 +65,27 @@ class TreeCache(object):
         return popped
 
     def values(self):
-        return [e.value for e in self.root.values()]
+        return list(iterate_tree_cache_entry(self.root))
 
     def __len__(self):
         return self.size
 
 
+def iterate_tree_cache_entry(d):
+    """Helper function to iterate over the leaves of a tree, i.e. a dict of that
+    can contain dicts.
+    """
+    if isinstance(d, dict):
+        for value_d in d.itervalues():
+            for value in iterate_tree_cache_entry(value_d):
+                yield value
+    else:
+        if isinstance(d, _Entry):
+            yield d.value
+        else:
+            yield d
+
+
 class _Entry(object):
     __slots__ = ["value"]
 

tests/storage/test__base.py

@@ -241,7 +241,7 @@ class CacheDecoratorTestCase(unittest.TestCase):
         callcount2 = [0]
 
         class A(object):
-            @cached(max_entries=2)
+            @cached(max_entries=20)  # HACK: This makes it 2 due to cache factor
             def func(self, key):
                 callcount[0] += 1
                 return key
@@ -258,6 +258,10 @@ class CacheDecoratorTestCase(unittest.TestCase):
         self.assertEquals(callcount[0], 2)
         self.assertEquals(callcount2[0], 2)
 
+        yield a.func2("foo")
+        self.assertEquals(callcount[0], 2)
+        self.assertEquals(callcount2[0], 2)
+
         yield a.func("foo3")
 
         self.assertEquals(callcount[0], 3)

tests/util/test_expiring_cache.py

@@ -0,0 +1,84 @@
+# -*- coding: utf-8 -*-
+# Copyright 2017 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.
+
+
+from .. import unittest
+
+from synapse.util.caches.expiringcache import ExpiringCache
+
+from tests.utils import MockClock
+
+
+class ExpiringCacheTestCase(unittest.TestCase):
+
+    def test_get_set(self):
+        clock = MockClock()
+        cache = ExpiringCache("test", clock, max_len=1)
+
+        cache["key"] = "value"
+        self.assertEquals(cache.get("key"), "value")
+        self.assertEquals(cache["key"], "value")
+
+    def test_eviction(self):
+        clock = MockClock()
+        cache = ExpiringCache("test", clock, max_len=2)
+
+        cache["key"] = "value"
+        cache["key2"] = "value2"
+        self.assertEquals(cache.get("key"), "value")
+        self.assertEquals(cache.get("key2"), "value2")
+
+        cache["key3"] = "value3"
+        self.assertEquals(cache.get("key"), None)
+        self.assertEquals(cache.get("key2"), "value2")
+        self.assertEquals(cache.get("key3"), "value3")
+
+    def test_iterable_eviction(self):
+        clock = MockClock()
+        cache = ExpiringCache("test", clock, max_len=5, iterable=True)
+
+        cache["key"] = [1]
+        cache["key2"] = [2, 3]
+        cache["key3"] = [4, 5]
+
+        self.assertEquals(cache.get("key"), [1])
+        self.assertEquals(cache.get("key2"), [2, 3])
+        self.assertEquals(cache.get("key3"), [4, 5])
+
+        cache["key4"] = [6, 7]
+        self.assertEquals(cache.get("key"), None)
+        self.assertEquals(cache.get("key2"), None)
+        self.assertEquals(cache.get("key3"), [4, 5])
+        self.assertEquals(cache.get("key4"), [6, 7])
+
+    def test_time_eviction(self):
+        clock = MockClock()
+        cache = ExpiringCache("test", clock, expiry_ms=1000)
+        cache.start()
+
+        cache["key"] = 1
+        clock.advance_time(0.5)
+        cache["key2"] = 2
+
+        self.assertEquals(cache.get("key"), 1)
+        self.assertEquals(cache.get("key2"), 2)
+
+        clock.advance_time(0.9)
+        self.assertEquals(cache.get("key"), None)
+        self.assertEquals(cache.get("key2"), 2)
+
+        clock.advance_time(1)
+        self.assertEquals(cache.get("key"), None)
+        self.assertEquals(cache.get("key2"), None)

tests/util/test_lrucache.py

@@ -93,7 +93,7 @@ class LruCacheCallbacksTestCase(unittest.TestCase):
         cache.set("key", "value")
         self.assertFalse(m.called)
 
-        cache.get("key", callback=m)
+        cache.get("key", callbacks=[m])
         self.assertFalse(m.called)
 
         cache.get("key", "value")
@@ -112,10 +112,10 @@ class LruCacheCallbacksTestCase(unittest.TestCase):
         cache.set("key", "value")
         self.assertFalse(m.called)
 
-        cache.get("key", callback=m)
+        cache.get("key", callbacks=[m])
         self.assertFalse(m.called)
 
-        cache.get("key", callback=m)
+        cache.get("key", callbacks=[m])
         self.assertFalse(m.called)
 
         cache.set("key", "value2")
@@ -128,7 +128,7 @@ class LruCacheCallbacksTestCase(unittest.TestCase):
         m = Mock()
         cache = LruCache(1)
 
-        cache.set("key", "value", m)
+        cache.set("key", "value", callbacks=[m])
         self.assertFalse(m.called)
 
         cache.set("key", "value")
@@ -144,7 +144,7 @@ class LruCacheCallbacksTestCase(unittest.TestCase):
         m = Mock()
         cache = LruCache(1)
 
-        cache.set("key", "value", m)
+        cache.set("key", "value", callbacks=[m])
         self.assertFalse(m.called)
 
         cache.pop("key")
@@ -163,10 +163,10 @@ class LruCacheCallbacksTestCase(unittest.TestCase):
         m4 = Mock()
         cache = LruCache(4, 2, cache_type=TreeCache)
 
-        cache.set(("a", "1"), "value", m1)
+        cache.set(("a", "1"), "value", callbacks=[m1])
-        cache.set(("a", "2"), "value", m2)
+        cache.set(("a", "2"), "value", callbacks=[m2])
-        cache.set(("b", "1"), "value", m3)
+        cache.set(("b", "1"), "value", callbacks=[m3])
-        cache.set(("b", "2"), "value", m4)
+        cache.set(("b", "2"), "value", callbacks=[m4])
 
         self.assertEquals(m1.call_count, 0)
         self.assertEquals(m2.call_count, 0)
@@ -185,8 +185,8 @@ class LruCacheCallbacksTestCase(unittest.TestCase):
         m2 = Mock()
         cache = LruCache(5)
 
-        cache.set("key1", "value", m1)
+        cache.set("key1", "value", callbacks=[m1])
-        cache.set("key2", "value", m2)
+        cache.set("key2", "value", callbacks=[m2])
 
         self.assertEquals(m1.call_count, 0)
         self.assertEquals(m2.call_count, 0)
@@ -202,14 +202,14 @@ class LruCacheCallbacksTestCase(unittest.TestCase):
         m3 = Mock(name="m3")
         cache = LruCache(2)
 
-        cache.set("key1", "value", m1)
+        cache.set("key1", "value", callbacks=[m1])
-        cache.set("key2", "value", m2)
+        cache.set("key2", "value", callbacks=[m2])
 
         self.assertEquals(m1.call_count, 0)
         self.assertEquals(m2.call_count, 0)
         self.assertEquals(m3.call_count, 0)
 
-        cache.set("key3", "value", m3)
+        cache.set("key3", "value", callbacks=[m3])
 
         self.assertEquals(m1.call_count, 1)
         self.assertEquals(m2.call_count, 0)
@@ -227,8 +227,33 @@ class LruCacheCallbacksTestCase(unittest.TestCase):
         self.assertEquals(m2.call_count, 0)
         self.assertEquals(m3.call_count, 0)
 
-        cache.set("key1", "value", m1)
+        cache.set("key1", "value", callbacks=[m1])
 
         self.assertEquals(m1.call_count, 1)
         self.assertEquals(m2.call_count, 0)
         self.assertEquals(m3.call_count, 1)
+
+
+class LruCacheSizedTestCase(unittest.TestCase):
+
+    def test_evict(self):
+        cache = LruCache(5, size_callback=len)
+        cache["key1"] = [0]
+        cache["key2"] = [1, 2]
+        cache["key3"] = [3]
+        cache["key4"] = [4]
+
+        self.assertEquals(cache["key1"], [0])
+        self.assertEquals(cache["key2"], [1, 2])
+        self.assertEquals(cache["key3"], [3])
+        self.assertEquals(cache["key4"], [4])
+        self.assertEquals(len(cache), 5)
+
+        cache["key5"] = [5, 6]
+
+        self.assertEquals(len(cache), 4)
+        self.assertEquals(cache.get("key1"), None)
+        self.assertEquals(cache.get("key2"), None)
+        self.assertEquals(cache["key3"], [3])
+        self.assertEquals(cache["key4"], [4])
+        self.assertEquals(cache["key5"], [5, 6])