性能问题.使用java从套接字读取字节时速度太慢

Question

这些天我在使用java socket时对Tcp性能感到困惑.实际上java代码非常简单.详情如下:

1. 服务器打开一个端口并开始监听.
2. 客户端请求和连接到服务器后,客户端开始写入套接字.
3. 在服务器获得请求后,它将打开一个新线程来处理此连接.(此连接是一个长时间连接,不会超时).
4. 服务器将继续读取,直到它到达结束分隔符,然后给客户端回复并继续继续阅读.
5. 在客户端获得响应后,它将再次发送另一个请求.

我发现客户端一次写入整个消息(包括结束分隔符),通信速度是否令人满意,速度可以达到每分钟50000条消息.但是,如果客户端在不同的时间内将字节写入套接字,速度会快速下降,每分钟只有1400条消息,这是原始速度的1/40倍.我很困惑.任何人都可以帮我一臂之力？任何评论表示赞赏!

我模拟的服务器端如下:

public class ServerForHelp {

    final static int BUFSIZE = 10240;
    Socket socket;
    String delimiter = "" + (char) 28 + (char) 13;

    public static void main(String[] args) throws IOException {

            ServerSocket ss = new ServerSocket(9200);
            System.out.println("begin to accept...");
            while (true) {
                Socket s = ss.accept();
                Thread t = new Thread(new SocketThread1(s));
                t.start();
            }
    }

    public String readUntilDelimiter() throws Exception {
        StringBuffer stringBuf = new StringBuffer();
        InputStream stream = socket.getInputStream();
        InputStreamReader reader = null;
        reader = new InputStreamReader(stream);

        char[] buf = new char[BUFSIZE];

        while (true) {
            int n = -1;
                n = reader.read(buf, 0, BUFSIZE);
            if (n == -1) {
                return null;  // it means the client has closed the connection, so return null.
            } else if (n == 0) {
                continue; // continue to read the data until got the delimiter from the socket.
            }

            stringBuf.append(buf, 0, n);
            String s = stringBuf.toString();

            int delimPos = s.indexOf(delimiter);
            if (delimPos >= 0) {
                // found the delimiter; return prefix of s up to separator and
                // To make the thing simple, I have discarded the content after the delimiter.
                String result = s.substring(0, delimPos);
                sendTheResponse(socket);
                return result;
            }
        }
    }

    private void sendTheResponse(Socket socket) throws IOException {
        Writer writer = new BufferedWriter(new OutputStreamWriter(socket.getOutputStream()));
        writer.write("Hi, From server response");
        writer.flush();
    }

}

class SocketThread1 implements Runnable {

    Socket socket;

    public SocketThread1(Socket socket) {
        this.socket = socket;
    }

    @Override
    public void run() {
        ServerForHelp server = new ServerForHelp();
        server.socket = socket;
        while (true) {
            try {
                if (server.readUntilDelimiter() == null) // it means that the client has closed the connection, exist
                    break;
            } catch (Exception e) {
                e.printStackTrace();
            }
        }
    }

}

这是一个正常的套接字编程.

以下是我的客户方:

public void execute() throws Exception{

        int msgCnt = 0;
        Socket socket = null;
        byte[] bufBytes = new byte[512];
        long start = 0;
        final char START_MESSAGE = 0x0B;
        final char END_MESSAGE = 0x1C;
        final char END_OF_RECORD = 0x0D;//\r
        String MESSAGE = "HELLO, TEST";
        socket = new Socket("192.168.81.39", 9200);
        OutputStream os = socket.getOutputStream();
        InputStream is = socket.getInputStream();

        while (System.currentTimeMillis() - start < 60000)
        {

            // If you send the total message at one time, the speed will be improved significantly  

            // FORMAT 1
            StringBuffer buf = new StringBuffer();
            buf.append(START_MESSAGE);
            buf.append(MESSAGE);
            buf.append(END_MESSAGE);
            buf.append(END_OF_RECORD);
            os.write(buf.toString().getBytes());
            // FORMAT 1 END

            //FORMAT 2
//        os.write(START_MESSAGE);
//        os.write(MESSAGES[port].getBytes());
//        os.write(END_MESSAGE);
//        os.write(END_OF_RECORD);
            //FORMAT 2 END
            os.flush();
            is.read(bufBytes);
            msgCnt++;

            System.out.println(msgCnt);
        }
        System.out.println( msgCnt + " messages per minute");
    }

如果我使用"格式1",发送消息,速度可以达到每分钟50000条消息,但如果使用"格式2",则速度降至每分钟1400条消息.谁清楚原因？

我试图尽可能详细地描述,任何帮助都将非常感激.

Answer 1

快速连续多次向套接字写入非常短的后续读取可能会触发Nagle算法与TCP延迟确认之间的错误交互; 即使您禁用Nagle算法,也会导致每个写入调用发送一个完整的数据包(开销超过40个字节,无论写入是一个字节还是一千个).

包装一个BufferedOutputStream套接字的输出流周围应该给你的性能类似"格式1"(正因为它拥有的东西在一个字节数组,直到填满或刷新).

正如John Nagle在Slashdot上解释的那样:

用户级解决方案是避免套接字上的写 - 读 - 读序列.write-read-write-read很好.写 - 写 - 写得很好.但写 - 写 - 读是一个杀手.所以,如果可以的话,将你的小写入缓冲到TCP并立即发送它们.