What did Segmenfault's message push backstage do? I know the front desk is definitely Ajax

First I want to know if this offline message exists in MySQL or in a NoSQL database?
Then I would like to know his update strategy.
For example, when the client is on-line, the client to the server to fetch data or the server to determine whether the user is online. Push the message to the client once it's online?

And did these read messages get erased from the database after they were read? Is it finished to delete or for example a scheduled task, such as the Daily 4 o'clock in the morning unified deletion of read messages?
Is this message sending module an asynchronous one? But I see a lot of news to remind the Open source program is synchronized. (There is no asynchronous framework such things, such as Wecenter, it seems that the use of php,php itself can not be asynchronous, the message is asynchronous or synchronous "to seek doubts!"
Because I do not understand this piece, said is also drunk.
The Great God doubts!

Reply content:

First I want to know if this offline message exists in MySQL or in a NoSQL database?
Then I would like to know his update strategy.
For example, when the client is on-line, the client to the server to fetch data or the server to determine whether the user is online. Push the message to the client once it's online?

And did these read messages get erased from the database after they were read? Is it finished to delete or for example a scheduled task, such as the Daily 4 o'clock in the morning unified deletion of read messages?
Is this message sending module an asynchronous one? But I see a lot of news to remind the Open source program is synchronized. (There is no asynchronous framework such things, such as Wecenter, it seems that the use of php,php itself can not be asynchronous, the message is asynchronous or synchronous "to seek doubts!"
Because I do not understand this piece, said is also drunk.
The Great God doubts!

1. Messages can exist inside MySQL, but unread message sequences can exist in NoSQL, and SF should be inside the redis.
2. There is no such a complicated idea, is the ordinary rotation, on-line from the server grabbed, rather than the server to push the client.
3. No, because you can see the read message from the message. However, SF clears old data, which means that an account can save up to 300 messages, which seems to be deleted earlier. Delete a message minutes of things, I personally feel no need to use the queue.
4. Because it's polling, not pushing, so here you talk about synchronous asynchrony doesn't seem to make sense. If you look at your example, SF should be the same.

Finally it feels like you've got the push and poll mixed up, the push is that the server is actively pushing messages to the client, and polling is the client requesting the server and then the server returns the message. These two mechanisms are not the same. If it is a push, it must be a message queue to let the server a push compared to cool.

He's not Ajax, it's websocket.

