Add app-local caching and stop using memcache; reduce overall datastore access.

api.py

@@ -54,6 +54,11 @@ def CreateChannel(google_user, client, instance_id, args):
 
 def Pin(google_user, client, instance_id, args):
   instance = models.Instance.FromID(instance_id)
+  if not instance or not instance.active:
+    # Probably a race with the channel opening
+    return {
+      'result': 'retry',
+    }
 
   subject = args['subject']
   message = args['message']

channel.py

@@ -46,17 +46,15 @@ class OnChannelDisconnect(webapp2.RequestHandler):
     instance_id = self.request.get('from')
     instance_key = db.Key.from_path('Instance', instance_id)
 
-    subscriptions = models.Subscription.all().filter('instance =', instance_key)
-    for subscription in subscriptions:
-      subscription.delete()
+    subscriptions = list(models.Subscription.all().filter('instance =', instance_key))
+    if subscriptions:
+      db.delete(subscriptions)
 
     pins = models.Pin.all().filter('instance =', instance_key)
     for pin in pins:
       pin.Delete()
 
-    instance = models.Instance.FromID(instance_id)
-    if instance:
-      instance.delete()
+    db.delete(instance_key)
 
 
 app = webapp2.WSGIApplication([

lib/auth.py

@@ -17,7 +17,6 @@ import hmac
 import random
 import string
 
-from google.appengine.api import memcache
 from google.appengine.ext import db
 
 
@@ -32,11 +31,11 @@ class AuthKey(db.Model):
 
 _KEY_CHARS = string.ascii_letters + string.digits
 _KEY_LENGTH = 64
+_AUTH_KEY = []
 
 def GetAuthKey():
-  auth_key = memcache.get('auth_key')
-  if auth_key:
-    return auth_key
+  if _AUTH_KEY:
+    return _AUTH_KEY[0]
 
   for key in AuthKey.all().filter('live =', True):
     auth_key = key.auth_key
@@ -45,7 +44,7 @@ def GetAuthKey():
     auth_key = ''.join(random.choice(_KEY_CHARS) for _ in xrange(_KEY_LENGTH))
     AuthKey(auth_key=auth_key).put()
 
-  memcache.set('auth_key', auth_key)
+  _AUTH_KEY.append(auth_key)
   return auth_key
 
 

lib/models.py

@@ -112,6 +112,8 @@ class Subject(db.Model):
 
   next_message_id = db.IntegerProperty(required=True, default=1)
 
+  _cache = {}
+
   @classmethod
   def _UpdateHashWithString(cls, hashobj, string):
     string = string.encode('utf8')
@@ -138,12 +140,20 @@ class Subject(db.Model):
     else:
       writable_only_by = None
 
-    return cls.get_or_insert(
-        cls._KeyName(subject),
+    key_name = cls._KeyName(subject)
+    obj = cls._cache.get(key_name)
+    if obj:
+      return obj
+
+    obj = cls.get_or_insert(
+        key_name,
         name=subject['name'],
         readable_only_by=readable_only_by,
         writable_only_by=writable_only_by)
 
+    cls._cache[key_name] = obj
+    return obj
+
   @db.transactional()
   def GetRecentMessages(self, num_messages):
     query = (