在谷歌应用程序引擎python上与memcache斗争

Question

我一直在努力让memcache在我的应用程序上运行一段时间.我以为我终于让它工作了,它永远不会从数据库中读取(除非memcache数据当然丢失),只是因为数据存储区读数过多而导致我的网站关闭!我目前正在使用免费的appspot,并希望尽可能长时间保持这种状态.无论如何,这是我的代码,也许有人可以帮我找到它的漏洞.

我目前正在尝试通过重写db.Model.all(),delete()和put()方法来首先查询memcache来实现memcache.我有memcache设置数据存储区中的每个对象都有自己的memcache值,其id为密钥.然后,对于每个Model类,我都有一个知道如何查询的键下的id列表.我希望我能够清楚地解释这一点.

""" models.py """
         @classmethod
         def all(cls, order="sent"):
                 result = get_all("messages", Message)
                 if not result or memcache.get("updatemessages"):
                         result = list(super(Message, cls).all())
                         set_all("messages", result)
                         memcache.set("updatemessages", False)
                         logging.info("DB Query for messages")

                 result.sort(key=lambda x: getattr(x, order), reverse=True)
                 return result

         @classmethod
         def delete(cls, message):
                 del_from("messages", message)
                 super(Message, cls).delete(message)

         def put(self):
                 super(Message, self).put()

                 add_to_all("messages", self)



""" helpers.py """

 def get_all(type, Class):
         all = []
         ids = memcache.get(type+"allid")
         query_amount = 0
         if ids:
                 for id in ids:
                         ob = memcache.get(str(id))
                         if ob is None:
                                 ob = Class.get_by_id(int(id))
                                 if ob is None:
                                         continue
                                 memcache.set(str(id), ob)
                                 query_amount += 1
                         all.append(ob)
                 if query_amount: logging.info(str(query_amount) + " ob queries")
                 return all
         return None

 def add_to_all(type, object):
         memcache.set(str(object.key().id()), object)
         all = memcache.get(type+"allid")
         if not all:
                 all = [str(ob.key().id()) for ob in object.__class__.all()]
                 logging.info("DB query for %s" % type)
         assert all is not None, "query returned None.  Send this error code to ____: 2 3-193A"
         if not str(object.key().id()) in all:
                 all.append(str(object.key().id()))
         memcache.set(type+"allid", all)

 @log_on_fail
 def set_all(type, objects):
         assert type in ["users", "messages", "items"], "set_all was not passed a valid type.  Send this error code to ____: 33-205"
         assert not objects is None, "set_all was passed None as the list of objects.    Send this error code to _________: 33-206"
         all = []
         for ob in objects:
                 error = not memcache.set(str(ob.key().id()), ob)
                 if error:
                         logging.warning("keys not setting properly. Object must not be pickleable")
                 all.append(str(ob.key().id()))
         memcache.set(type+"allid", all)

 @log_on_fail
 def del_from(type, object):
         all = memcache.get(type+"allid")
         if not all:
                 all = object.__class__.all()
                 logging.info("DB query %s" % type)
         assert all, "Could not find any objects.  Send this error code to _____: 13-    219"
         assert str(object.key().id()) in all, "item not found in cache.  Send this error code to ________: 33-220"
         del all[ all.index(str(object.key().id())) ]
         memcache.set(type+"allid", all)
         memcache.delete(str(object.key().id()))

我为所有的混乱和缺乏优雅道歉.希望有人能够提供帮助.我已经考虑过切换到ndb但是现在我宁愿坚持我的自定义缓存.你会注意到的logging.info("some-number of ob queries").我经常得到这个日志.也许每半小时一两次.memcache真的丢失了我的代码常常或有问题的数据吗？

Answer 1

简单的解决方案:切换到NDB.

NDB模型将值存储在memcache和实例缓存中(100%免费),当您更新/删除对象时,这些模型也会使缓存无效.Retrieval将首先尝试从实例缓存中获取,然后如果从memcache失败,最后从数据存储中失败,它将在上升过程中错过的任何缓存中设置值.