Rename lib/message_cache.py to lib/cache_helpers.py

(imported from commit 591e427aee47aea58b50d6c3fbd6a05cfe9378ea)

zephyr/lib/cache_helpers.py

@@ -0,0 +1,23 @@
+# This file needs to be different from cache.py because cache.py
+# cannot import anything from zephyr.models or we'd have an import
+# loop
+from zephyr.models import Message
+from zephyr.lib.cache import cache_with_key, djcache, message_cache_key
+
+MESSAGE_CACHE_SIZE = 25000
+
+def cache_save_message(message):
+    djcache.set(message_cache_key(message.id), (message,), timeout=3600*24)
+
+@cache_with_key(message_cache_key)
+def cache_get_message(message_id):
+    return Message.objects.select_related("client", "sender").get(id=message_id)
+
+# Called on Tornado startup to ensure our message cache isn't empty
+def populate_message_cache():
+    items_for_memcached = {}
+    for m in Message.objects.select_related("sender", "client").all().order_by(
+        "-id")[0:MESSAGE_CACHE_SIZE]:
+        items_for_memcached[message_cache_key(m.id)] = (m,)
+
+    djcache.set_many(items_for_memcached, timeout=3600*24)