RPCRequests and datastore

I'm getting started with Google App Engine. I want to make an AJAX chat.

class ChatMessage(db.Model):
  message = db.StringProperty()
  created = db.DateTimeProperty(auto_now_add=True)

class RPCHandler(webapp.RequestHandler):
  ##get message every 4 seconds
  def get(self):
    que = db.Query(ChatMessage).order('-created')
    chat_list = que.fetch(limit=3)
    jencoded_chat_list = gaejsonEncoder.encode(chat_list) ##my own module
    self.response.out.write(jencoded_chat_list)

RESULT: message3,message2,message1

This is　what I intended.

I wanted to add POST ajax Request, so added RPCHandler2.

class RPCHandler2(webapp.RequestHandler):
  def post(self):
    msg = self.request.get('message')
    if msg == '':
        return
    newchat = ChatMessage(message=msg)
    newchat.put()

    que = db.Query(ChatMessage).order('-created')
    chat_list =开发者_Python百科 que.fetch(limit=3))
    jencoded_chat_list = gaejsonEncoder.encode(chat_list)
    self.response.out.write(jencoded_chat_list)

I write "POST Message!" in textarea and click the button,

RESULT: POST Message!,message3,message2

This is what I wanted.

But 4 seconds later, 'GET' started and

RESULT: message3,message2,message1

Why 'GET' couldn't get the new message from datastore?

Thanks in advance.

If you are using the high replication datastore you might be facing an "eventual consistency" problem. The datastore replica handling the get request may not have received the recently submitted data yet.

If you put the newchat.put() inside of a transaction it's more likely that future gets will be consistent.