Retrieve message objects from memcached in a bulk request.

On my laptop, this saves about 80 milliseconds per 1000 messages
requested via get_old_messages queries.  Since we only have one
memcached process and it does not run with special priority, this
might have significant impact on load during server restarts.

(imported from commit 06ad13f32f4a6d87a0664c96297ef9843f410ac5)

zephyr/lib/cache.py

@@ -67,6 +67,13 @@ def cache_with_key(keyfunc, cache_name=None, timeout=None):
 
     return decorator
 
+def cache_get_many(keys, cache_name=None):
+    if cache_name is None:
+        cache_backend = djcache
+    else:
+        cache_backend = get_cache(cache_name)
+    return cache_backend.get_many(keys)
+
 def cache(func):
     """Decorator which applies Django caching to a function.