什麼是消費端的限流?
假設一個場景,首先我們RabbitMQ服務器有上萬條未處理的消息,我們隨便打開一個消費者客戶端,會出現下面情況:巨量的消息瞬間全部圖送過來,但是我們單個客戶端無法同時處理這麼多數據!
RabbitMQ提供了一種qos(服務質量保證)功能,即在非自動確認消息的前提下,如果一定數目的消息(通過基於consume或者channel設置Qos的值)未被確認前,不進行消費。
void BasicQos(unit prefecthSize,ushort prefetchCount,bool global);
prefecthSize:0
prefetchCount:會告訴RabbitMQ不要同時給一個消費者推送對於N個消息,即一旦有N個消息還沒有ack,則該Consumer講block掉,直到有消息ack
global:true/false是否將上面設置應用於channel,簡單來說就是上面限制是channel級別還是consumer級別。
注意:
prefechSize和global這兩項,RabbitMQ沒有實現,暫不研究,prefetchCount在no_ask=false的情況下生效,即在自動應答的情況下這兩個值是不生效的。
消費者端代碼
package com.star.movie.limit;
import com.rabbitmq.client.AMQP;
import com.rabbitmq.client.Channel;
import com.rabbitmq.client.DefaultConsumer;
import com.rabbitmq.client.Envelope;
import java.io.IOException;
/**
* @Description:
* @author:kaili
* @Date: 2019-04-22 18:22
**/
public class MyLimitConsumer extends DefaultConsumer {
private Channel channel;
public MyLimitConsumer(Channel channel) {
super(channel);
this.channel = channel;
}
@Override
public void handleDelivery(String consumerTag, Envelope envelope, AMQP.BasicProperties properties, byte[] body) throws IOException {
System.err.println("-----------consume message----------");
System.err.println("consumerTag: " + consumerTag);
System.err.println("envelope: " + envelope);
System.err.println("properties: " + properties);
System.err.println("body: " + new String(body));
channel.basicAck(envelope.getDeliveryTag(), false);
}
}
package com.star.movie.limit;
import com.rabbitmq.client.Channel;
import com.rabbitmq.client.Connection;
import com.star.movie.common.Constant;
/**
* @Description:
* @author:kaili
* @Date: 2019-04-22 18:17
**/
public class LimitConsumer {
public static void main(String[] args) throws Exception {
Connection connection = Constant.getConnection();
Channel channel = connection.createChannel();
String exchangeName = "test_qos_exchange";
String queueName = "test_qos_queue";
String routingKey = "qos.#";
channel.exchangeDeclare(exchangeName, "topic", true, false, null);
channel.queueDeclare(queueName, true, false, false, null);
channel.queueBind(queueName, exchangeName, routingKey);
//1 限流方式 第一件事就是 autoAck設置爲 false
channel.basicQos(0,1,false);
channel.basicConsume(queueName,false,new MyLimitConsumer(channel));
}
}
生產者代碼
package com.star.movie.limit;
import com.rabbitmq.client.Channel;
import com.rabbitmq.client.Connection;
import com.star.movie.common.Constant;
/**
* @Description:
* @author:kaili
* @Date: 2019-04-22 18:16
**/
public class LimitProducer {
public static void main(String[] args) throws Exception{
Connection connection = Constant.getConnection();
Channel channel = connection.createChannel();
String exchange = "test_qos_exchange";
String routingKey = "qos.save";
String msg = "Hello RabbitMQ QOS Message";
for(int i =0; i<5; i ++){
channel.basicPublish(exchange, routingKey, true, null, msg.getBytes());
}
}
}