Usage scenarios of php long connection and short connection

Short connection

Connect->Transfer data->Close connection

For example HTTP is a stateless short link. Each time the browser and server perform an HTTP operation, a connection is established, but the connection is terminated when the task is completed.

Specifically, the browser client initiates and establishes a TCP connection -> client sends an HttpRequest message -> server receives the message ->server handle and sends an HttpResponse message to the front end, which is called immediately after sending socket.close method->client receives the response message->client will eventually receive a signal from the server to disconnect the TCP connection->client disconnects the TCP connection, specifically by calling the close method. (Recommended learning: PHP programming from entry to proficiency)

It can also be said: short connection means that after SOCKET is connected, the connection is disconnected immediately after sending and receiving data.

Because the connection is disconnected after receiving the data, there will be no contact each time the data is accepted and processed. This is one of the reasons why the HTTP protocol is stateless.

Long connection

Connect->Transfer data->Keep connection->Transfer data-> ........... ->Until one party closes the connection, possibly the client closes the connection.

Long connection means that after establishing a SOCKET connection, the connection will be maintained regardless of whether it is used or not, but the security is poor.

HTTP’s choice of short links and long connections:

HTTP is stateless, that is to say, every time the browser and server perform an HTTP operation, A connection is established once, but the connection is terminated when the task is completed. If an HTML or other type of Web page accessed by the client browser contains other Web resources, such as JavaScript files, image files, CSS files, etc.; every time the browser encounters such a Web resource, it will create a HTTP Session

Compared with HTTP1.1 and HTTP1.0, the biggest difference is the addition of persistent connection support (it seems that the latest HTTP1.1 can explicitly specify keep-alive), but it is still stateless. , or cannot be trusted.

If the browser or server adds this line of code Connection:keep-alive

The TCP connection will remain open after sending, so the browser can continue to pass the same connection to send a request. Keeping connections saves the time required to establish a new connection for each request and also saves bandwidth.

To achieve long connections, both the client and the server must support long connections.

When to use long connection and short connection?

Long connections are mostly used for frequent operations, point-to-point communication, and the number of connections cannot be too many. Each TCP connection requires a three-step handshake, which takes time. If each operation is connected first and then operated, the processing speed will be reduced a lot, so it will not be disconnected after each operation, and the processing will be done directly It's OK to send the data packet without establishing a TCP connection.

For example: the database connection uses a long connection. Frequent communication with a short connection will cause socket errors, and frequent socket creation is also a waste of resources.

HTTP services like WEB websites generally use short links, because long connections will consume a certain amount of resources for the server, and like WEB websites, thousands or even hundreds of millions of them are frequently used. Using a short connection for the client connection will save some resources. If you use a long connection and there are thousands of users at the same time, it is conceivable if each user occupies one connection. Therefore, the amount of concurrency is large, but each user needs to use a short connection if they do not need frequent operations.

In short, the choice of long connection and short connection depends on the situation.

For specific network applications:

http 1.0一般就指短连接，smtp,pop3,telnet这种就可以认为是长连接。一般的网络游戏应用都是长连接

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