diff --git a/aiocache/backends/memory.py b/aiocache/backends/memory.py
index e2ddf03a..fdfd567d 100644
--- a/aiocache/backends/memory.py
+++ b/aiocache/backends/memory.py
@@ -79,9 +79,10 @@ async def _delete(self, key, _conn=None):
         return self.__delete(key)
 
     async def _clear(self, namespace=None, _conn=None):
+        """Empty the cache for the namespace provided or the entire cache"""
         if namespace:
             for key in list(SimpleMemoryBackend._cache):
-                if key.startswith(namespace):
+                if self.key_filter(key, namespace):
                     self.__delete(key)
         else:
             SimpleMemoryBackend._cache = {}
diff --git a/aiocache/base.py b/aiocache/base.py
index d8481092..d3370415 100644
--- a/aiocache/base.py
+++ b/aiocache/base.py
@@ -98,6 +98,13 @@ class BaseCache:
         the backend. Default is None
     :param key_builder: alternative callable to build the key. Receives the key and the namespace
         as params and should return something that can be used as key by the underlying backend.
+    :param key_filter: callable that returns `True` if the specified key is 
+        in the specified namespace. Callable signature must be:
+        `key_filter(key, namespace)`.
+        This callable is complementary to the `key_builder` callable.
+        If `key_builder` is provided, `key_filter` should also be provided.
+        If `key_filter` is not provided, default behavior will be compatible
+        with the default behavior of `key_builder`.
     :param timeout: int or float in seconds specifying maximum timeout for the operations to last.
         By default its 5. Use 0 or None if you want to disable it.
     :param ttl: int the expiration time in seconds to use as a default in all operations of
@@ -107,12 +114,13 @@ class BaseCache:
     NAME: str
 
     def __init__(
-        self, serializer=None, plugins=None, namespace=None, key_builder=None, timeout=5, ttl=None
+        self, serializer=None, plugins=None, namespace=None, key_builder=None, key_filter=None, timeout=5, ttl=None
     ):
         self.timeout = float(timeout) if timeout is not None else timeout
         self.namespace = namespace
         self.ttl = float(ttl) if ttl is not None else ttl
         self.build_key = key_builder or self._build_key
+        self.key_filter = key_filter or self._key_filter
 
         self._serializer = None
         self.serializer = serializer or serializers.StringSerializer()
@@ -488,6 +496,10 @@ def _build_key(self, key, namespace=None):
             return "{}{}".format(self.namespace, key)
         return key
 
+    def _key_filter(self, key, namespace):
+        """Return True if key is in namespace"""
+        return key.startswith(namespace)
+
     def _get_ttl(self, ttl):
         return ttl if ttl is not SENTINEL else self.ttl
 
diff --git a/aiocache/decorators.py b/aiocache/decorators.py
index 202a45cc..90a39d04 100644
--- a/aiocache/decorators.py
+++ b/aiocache/decorators.py
@@ -136,14 +136,16 @@ def _key_from_args(self, func, args, kwargs):
 
     async def get_from_cache(self, key):
         try:
-            value = await self.cache.get(key)
+            namespace = self._kwargs.get("namespace", None)
+            value = await self.cache.get(key, namespace=namespace)
             return value
         except Exception:
             logger.exception("Couldn't retrieve %s, unexpected error", key)
 
     async def set_in_cache(self, key, value):
         try:
-            await self.cache.set(key, value, ttl=self.ttl)
+            namespace = self._kwargs.get("namespace", None)
+            await self.cache.set(key, value, namespace=namespace, ttl=self.ttl)
         except Exception:
             logger.exception("Couldn't set %s in key %s, unexpected error", value, key)
 
@@ -205,7 +207,12 @@ async def decorator(self, f, *args, **kwargs):
 
 
 def _get_cache(cache=Cache.MEMORY, serializer=None, plugins=None, **cache_kwargs):
-    return cache(serializer=serializer, plugins=plugins, **cache_kwargs)
+    return Cache(
+        cache, 
+        serializer=serializer, 
+        plugins=plugins, 
+        **cache_kwargs,
+    )
 
 
 def _get_args_dict(func, args, kwargs):
diff --git a/aiocache/plugins.py b/aiocache/plugins.py
index efbb4311..efa11092 100644
--- a/aiocache/plugins.py
+++ b/aiocache/plugins.py
@@ -60,12 +60,15 @@ async def do_save_time(self, client, *args, took=0, **kwargs):
     )
 
 
-class HitMissRatioPlugin(BasePlugin):
+class _HitMissRatioPlugin(BasePlugin):
     """
-    Calculates the ratio of hits the cache has. The data is saved in the cache class as a dict
-    attribute called ``hit_miss_ratio``. For example, to access the hit ratio of the cache,
-    you can do ``cache.hit_miss_ratio['hit_ratio']``. It also provides the "total" and "hits"
-    keys.
+    Calculates the ratio of hits the cache has. The data is saved in the 
+    cache class as a dict attribute called ``hit_miss_ratio``. 
+    For example, to access the hit ratio of the cache,
+    you can do ``cache.hit_miss_ratio['hit_ratio']``. 
+    It also provides the "total" and "hits" keys.
+
+    :param key: str should already include the namespace, if available
     """
 
     async def post_get(self, client, key, took=0, ret=None, **kwargs):
@@ -96,3 +99,22 @@ async def post_multi_get(self, client, keys, took=0, ret=None, **kwargs):
         client.hit_miss_ratio["hit_ratio"] = (
             client.hit_miss_ratio["hits"] / client.hit_miss_ratio["total"]
         )
+
+
+class HitMissRatioPlugin(_HitMissRatioPlugin):
+    """
+    Calculates the ratio of hits the cache has. The data is saved in the 
+    cache class as a dict attribute called ``hit_miss_ratio``. 
+    For example, to access the hit ratio of the cache,
+    you can do ``cache.hit_miss_ratio['hit_ratio']``. 
+    It also provides the "total" and "hits" keys.
+
+    :param key: str should not include the namespace
+    """
+
+    async def post_get(self, client, key, took=0, ret=None, **kwargs):
+        """Update cache stats; use namespace if available"""
+        namespace = kwargs.get("namespace", None)
+        ns_key = client.build_key(key, namespace=namespace)
+        await super().post_get(client, ns_key, took=took, ret=ret, **kwargs)
+        return