Speed up cache size calculation

Instead of calculating the size of the cache repeatedly, which can take
a long time now that it can use a callback, instead cache the size and
update that on insertion and deletion.

This requires changing the cache descriptors to have two caches, one for
pending deferreds and the other for the actual values. There's no reason
to evict from the pending deferreds as they won't take up any more
memory.

5 files changed, 128 insertions, 46 deletions

diff --git a/synapse/util/caches/descriptors.py b/synapse/util/caches/descriptors.py
index d082c26b1f..b3b2d6092d 100644
--- a/synapse/util/caches/descriptors.py
+++ b/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, popped_to_iterator
 from synapse.util.logcontext import (
     PreserveLoggingContext, preserve_context_over_deferred, preserve_context_over_fn
 )
@@ -42,11 +42,23 @@ _CacheSentinel = object()
 CACHE_SIZE_FACTOR = float(os.environ.get("SYNAPSE_CACHE_FACTOR", 0.1))
 
 
-def deferred_size(deferred):
-    if deferred.called:
-        return len(deferred.result)
-    else:
-        return 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):
@@ -58,13 +70,16 @@ class Cache(object):
         "sequence",
         "thread",
         "metrics",
+        "_pending_deferred_cache",
     )
 
     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,
-            size_callback=deferred_size if iterable else None,
+            size_callback=(lambda d: len(d.result)) if iterable else None,
         )
 
         self.name = name
@@ -84,7 +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
@@ -96,15 +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:
-            # Only update the cache if the caches sequence number matches the
-            # number that the cache had before the SELECT was started (SYN-369)
-            self.prefill(key, value, callback=callback)
+        entry = CacheEntry(
+            deferred=value,
+            sequence=self.sequence,
+            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()
@@ -116,6 +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):
@@ -127,6 +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 popped_to_iterator(entry_dict):
+                entry.invalidate()
+
     def invalidate_all(self):
         self.check_thread()
         self.sequence += 1
@@ -254,11 +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,
@@ -272,7 +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())
 
@@ -370,7 +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
 
@@ -393,8 +444,8 @@ class CacheListDescriptor(object):
 
                     key = list(keyargs)
                     key[self.list_pos] = arg
-                    cache.update(
-                        sequence, tuple(key), observer,
+                    cache.set(
+                        tuple(key), observer,
                         callback=invalidate_callback
                     )
 
diff --git a/synapse/util/caches/dictionary_cache.py b/synapse/util/caches/dictionary_cache.py
index b0ca1bb79d..cb6933c61c 100644
--- a/synapse/util/caches/dictionary_cache.py
+++ b/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
diff --git a/synapse/util/caches/expiringcache.py b/synapse/util/caches/expiringcache.py
index b9ead9cbd5..2987c38a2d 100644
--- a/synapse/util/caches/expiringcache.py
+++ b/synapse/util/caches/expiringcache.py
@@ -56,6 +56,8 @@ class ExpiringCache(object):
 
         self.iterable = iterable
 
+        self._size_estimate = 0
+
     def start(self):
         if not self._expiry_ms:
             # Don't bother starting the loop if things never expire
@@ -70,9 +72,14 @@ 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:
-            self._cache.popitem(last=False)
+            _key, value = self._cache.popitem(last=False)
+            if self.iterable:
+                self._size_estimate -= len(value.value)
 
     def __getitem__(self, key):
         try:
@@ -109,7 +116,9 @@ 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",
@@ -118,7 +127,7 @@ class ExpiringCache(object):
 
     def __len__(self):
         if self.iterable:
-            return sum(len(value.value) for value in self._cache.itervalues())
+            return self._size_estimate
         else:
             return len(self._cache)
 
diff --git a/synapse/util/caches/lrucache.py b/synapse/util/caches/lrucache.py
index 00ddf38290..f1de034444 100644
--- a/synapse/util/caches/lrucache.py
+++ b/synapse/util/caches/lrucache.py
@@ -58,12 +58,6 @@ class LruCache(object):
 
         lock = threading.Lock()
 
-        def cache_len():
-            if size_callback is not None:
-                return sum(size_callback(node.value) for node in cache.itervalues())
-            else:
-                return len(cache)
-
         def evict():
             while cache_len() > max_size:
                 todelete = list_root.prev_node
@@ -78,6 +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
@@ -86,6 +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
@@ -104,23 +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.add(callback)
+                node.callbacks.update(callbacks)
                 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:
@@ -128,17 +137,16 @@ class LruCache(object):
                         cb()
                     node.callbacks.clear()
 
-                if callback:
-                    node.callbacks.add(callback)
+                    if size_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:
-                    callbacks = set([callback])
-                else:
-                    callbacks = set()
-                add_node(key, value, callbacks)
+                add_node(key, value, set(callbacks))
 
             evict()
 
diff --git a/synapse/util/caches/treecache.py b/synapse/util/caches/treecache.py
index c31585aea3..460e98a92d 100644
--- a/synapse/util/caches/treecache.py
+++ b/synapse/util/caches/treecache.py
@@ -65,12 +65,24 @@ class TreeCache(object):
         return popped
 
     def values(self):
-        return [e.value for e in self.root.values()]
+        return list(popped_to_iterator(self.root))
 
     def __len__(self):
         return self.size
 
 
+def popped_to_iterator(d):
+    if isinstance(d, dict):
+        for value_d in d.itervalues():
+            for value in popped_to_iterator(value_d):
+                yield value
+    else:
+        if isinstance(d, _Entry):
+            yield d.value
+        else:
+            yield d
+
+
 class _Entry(object):
     __slots__ = ["value"]