Handling the exception in my scheduler Class

Question

I have written a scheduler class which can schedule a batch job to run every 15 min. I wish to handle a scenario - if there is any exception during scheduling I do not want the chaining of scheduled job to be aborted. The job should keep on getting scheduled even there any error somewhere in the code.

public class abcSchClass implements Schedulable{

   Integer timeInterval;

   public abcSchClass(Integer timeInterval){
       this.timeInterval = timeInterval;
   }

   public void execute(SchedulableContext sc) {  
        try{
        // Re-schedule 
        System.debug('Enter Scheduler class');
        DateTime now  = DateTime.now();
        DateTime nextRunTime = now.addMinutes(timeInterval);
        String cronString = '' + nextRunTime.second() + ' ' + nextRunTime.minute() + ' ' + 
            nextRunTime.hour() + ' ' + nextRunTime.day() + ' ' + 
            nextRunTime.month() + ' ? ' + nextRunTime.year(); 
        System.schedule(abcSchClass.class.getName() + '-' + now.format(), cronString, new abcSchClass(timeInterval));
        // Abort the current job
        Id jobId = sc.getTriggerId();
        System.abortJob(jobId);     
        // Launch the replacement order batch job
        abcbatch b = new abcbatch(); 
        database.executebatch(b);
        system.debug('done scheduling');
        }
        catch(MyExceptionClass e){

        }
   }

}

I just need to run this code from Execute anonymous and it starts scheduling itself every 15 min. How can I handle the exception here? If there is any error in scheduling the current job then the subsequent scheduling should not be aborted permanently. Also I have built my own custom exception to manager exception. Below is my exception class

public class MyExceptionClass extends Exception {
    public MyExceptionClass( Exception e, string sourceClass){   
        throw(e);
    }
}

How can I use this exception class to manage my exception/error scenarios?

Answer 1

This is realistically impossible. The reason why, of course, is Governor Limits. The way your code is written, if a governor limit hits you, you're dead in the water, indefinitely, until someone creates a new job to start over.

Your best bet would be to simply schedule four jobs that run hourly, 15 minutes apart from each other. While that does seem kind of greedy, it does offer some modicum of reliability, because you're guaranteed to pick up correctly on the next 15 minute window.

That said, if you want maximum reliability, this is one of those times where you probably want to catch Exception (but, make sure you report the errors somewhere!).

The approximate pseudocode for resilient scheduling would look like the following.

public void execute(SchedulableContext context) {
    try {
        executeBatchJob();
    } catch(Exception e) {
        reportException(e);
    }
    try {
        rescheduleIn15Minutes(context);
    } catch(Exception e) {
        reportException(e);
    }
}

Instead of creating a cron job string that only works for the next run, instead schedule it to run with wildcards, like this:

String cronString = '0 '+ nextRun.minute()+' * * * ?';

This means that, even with a governor limit halt, your code will be delayed for an hour instead of dying off never to come back again.

As a further concept, perhaps you could simply create a job that runs hourly, and leverages scheduleBatch instead:

public void execute(SchedulableContext context) {
    try {
        abcbatch batch = new abcbatch();
        Database.executeBatch(batch);
        System.scheduleBatch(batch, 'Now+15', 15);
        System.scheduleBatch(batch, 'Now+30', 30);
        System.scheduleBatch(batch, 'Now+45', 45);
    } catch(Exception e) {
    }
}

Which will allow you to at least kick off the jobs, and the scheduler will simply remain scheduled hourly using the cron string "0 0 * * * ?".

Answer 2

I suggest you pause and think about what kind of exception it is that you're trying to "catch". If you encounter a governor limit exception, the scenario you're trying to create won't cover you. You'd need to do a getlimits() first of some kind for the type of limit (see Limits Class) you expect to exceed before you scheduled your job. Unfortunately, there isn't one for Chron Jobs. You'd need to check query limits first, query the chron job object, then also check the flex queue and so forth along with a host of other things. Catching gross "pokeman" exceptions can be ill advised.