Distributed scheduling problem

1、 The scene of timing task

Timing task form ： Every once in a while / A particular ⼀ Execute at all times

for example ：

• Order review 、 Out of stock
• Order timeout ⾃ Dynamic cancellation 、 Payment refund
• Gift certificate synchronization 、 Generate 、 Issue the homework
• Logistics information push 、 Grab job 、 Return and exchange processing
• Data backlog monitoring 、 Log monitoring 、 Service availability probe job
• Back up data regularly
• The financial system makes regular settlement every day
• Data archiving 、 Cleaning operations
• report form 、 Offline data analysis job

2、 What is distributed scheduling

What is distributed task scheduling ？ There are two meanings  

1） Scheduling tasks running in a distributed cluster environment （ Same as ⼀ Deploy multiple copies of a scheduled task program , There should only be ⼀ Scheduled tasks are executing ）

2） Distributed scheduling —> Distributed scheduling of scheduled tasks —> Splitting of scheduled tasks （ That is to say ⼀ individual ⼤ The job task of is divided into several small job tasks , At the same time ）

3、 The difference between scheduled tasks and message queues  

Common ground

• Asynchronous processing
  • Such as registration 、 Order event
• Should be ⽤ decoupling
  • Whether it's a scheduled task or a job MQ Both can be used as gears between two applications to realize application decoupling , This gear can transfer data , Of course, individual services do not need to consider these , When splitting a service, you often consider
• Traffic peak clipping
  • On double eleven , Tasks and assignments MQ Fine ⽤ To carry traffic , The back-end system processes orders regularly according to the service capacity or from MQ Grab an order. If an order arrival event is retrieved, the processing will be triggered , For front-end users, the result is that the order has been placed successfully , The order will not be affected

Different in nature

• Timed tasks are time driven , and MQ It's event driven ;
• Time driven is irreplaceable , For example, the daily interest settlement of the financial system , Not interest ⼀ strip （ Interest arrival event ） Even if the ⼀ Next , It is often calculated in batches through scheduled tasks ;
• therefore , Timed task jobs tend to be batch processing ,MQ Tends to deal with each item ;

4、 Implementation of scheduled tasks

There are many ways to implement timed tasks . In the early days when there was no timed task framework , We will use JDK Medium Timer Mechanism and multithreading mechanism （Runnable+ Thread to sleep ） To achieve timing or interval ⼀ Execute a certain for a period of time ⼀ This program ; Then came the timed task framework , For example, famous Quartz Task scheduling framework , send ⽤ Time expression （ Include ： second 、 branch 、 when 、 Japan 、 Zhou 、 year ） Configure a ⼀ When to perform a task ：

Task scheduling framework Quartz review

introduce jar

<!-- Task scheduling framework quartz-->
<!-- https://mvnrepository.com/artifact/org.quartz-scheduler/quartz -->
<dependency>
    <groupId>org.quartz-scheduler</groupId>
    <artifactId>quartz</artifactId>
    <version>2.3.2</version>
</dependency>

Scheduled task job main scheduler

import org.quartz.*;
import org.quartz.impl.StdSchedulerFactory;

public class QuartzMan {
    //  Create task scheduler 
    private static Scheduler createScheduler() throws SchedulerException {
        StdSchedulerFactory stdSchedulerFactory = new StdSchedulerFactory();
        Scheduler scheduler = stdSchedulerFactory.getScheduler();
        return scheduler;
    }

    //  Create a task 
    private static JobDetail creatJob() {
        JobBuilder jobBuilder = JobBuilder.newJob(demoJob.class); // TODO  Custom task class 
        jobBuilder.withIdentity("jobName", "myJob");
        JobDetail jobDetail = jobBuilder.build();
        return jobDetail;
    }

    /**
     *  Create job task time trigger （ Similar to bus ⻋ Out ⻋ schedule ）
     * cron The expression consists of seven positions , The blank space to separate 
     * 1、Seconds（ second ） 0~59
     * 2、Minutes（ branch ） 0~59
     * 3、Hours（⼩ when ） 0~23
     * 4、Day of Month（ God ）1~31, Note that there are ⽉ Copy no ⾜31 God 
     * 5、Month（⽉） 0~11, perhaps  JAN,FEB,MAR,APR,MAY,JUN,JUL,AUG,SEP,OCT,NOV,DEC
     * 6、Day of Week( Zhou ) 1~7,1=SUN  perhaps  SUN,MON,TUE,WEB,THU,FRI,SAT
     * 7、Year（ year ）1970~2099  optional 
     * Example ：
     * 0 0 11 * * ?  Daily 11 Click to trigger execution ⾏⼀ Time 
     * 0 30 10 1 * ?  Every time ⽉1 morning 10 Half past ten triggers execution ⾏⼀ Time 
     */
    public static Trigger createTrigger() {
        //  Create time trigger 
        CronTrigger cronTrigger = TriggerBuilder.newTrigger()
                .withIdentity("triggerName", "myTrigger")
                .startNow()
                .withSchedule(CronScheduleBuilder.cronSchedule("*/2 * * * * ?")).build();
        return cronTrigger;
    }

    public static void main(String[] args) throws SchedulerException {
        //  Create task scheduler 
        Scheduler scheduler = QuartzMan.createScheduler();
        //  Create a task 
        JobDetail job = QuartzMan.creatJob();
        //  Create job task time trigger 
        Trigger trigger = QuartzMan.createTrigger();
        //  Use the task scheduler to execute our tasks according to the time trigger 
        scheduler.scheduleJob(job, trigger);
        scheduler.start();
    }
}

Define a job, Need to implement Job Interface

import org.quartz.Job;
import org.quartz.JobExecutionContext;
import org.quartz.JobExecutionException;

public class demoJob implements Job {

    @Override
    public void execute(JobExecutionContext jobExecutionContext) throws JobExecutionException {
        System.out.println(" The keyboard is broken , The monthly salary is over ten thousand ");
    }
}

above , Is to review the task scheduling framework Quartz The general usage of , Then use in a distributed architecture environment Quartz Can't better meet our needs , We can use professional distributed scheduling framework , Here we recommend Elastic-job.