Different ways to schedule Batch Class

1.      Write a schedulable class for your Batch class.

·         Lets us assume my batch class name is SFDC_ExecuteAccountBatch.

·         To schedule it we need to create a new class and implement a schedulable interface

·         Syntax:

global with sharing class SFDC_ExecuteAccountBatchScheduler implements Schedulable {

    global void execute(SchedulableContext sc) {

                 SFDC_ExecuteAccountBatch b = new SFDC_ExecuteAccountBatch();
               database.executebatch(b);

    }

}

2.      Write a batch class with Schedulable interface

·         To avoid writing extra class we can implement a schedulable interface in batch class to make it easy and maintainable.

·         Syntax:

global class SFDC_ExecuteAccountBatch implements Database.Batchable<SObject>, Schedulable {

                global Database.QueryLocator start(Database.BatchableContext BC) {

                                // query on  required object and return Database.QueryLocator

                }

                global void execute(Database.BatchableContext BC, 

                               List<Sobject> scope) { // execute method

                // for batch class

// do you processing here

                                          }

                                           global void execute(SchedulableContext sc){ // execute method for

                                                                // schedulable interface

                                                                //execute your batch class here

                `                                               SFDC_ExecuteAccountBatch b = 

                                                                          new SFDC_ExecuteAccountBatch();
                                                               database.executebatch(b);

                                            }

                                            global void finish(Database.BatchableContext BC) {

                                                                // do completion activity like sending email

                                            }

}

Important Batch Apex Governor Limits

• Up to 5 batch jobs can be queued or active concurrently.
• Up to 100 Holding batch jobs can be held in the Apex flex queue.
• In a running test, you can submit a maximum of 5 batch jobs.

Best Practice

• Use extreme care if you are planning to invoke a batch job from a trigger. You must be able to guarantee that the trigger does not add more batch jobs than the limit.
• Use Database.Stateful with the class definition if you want to share instance member variables or data across job transactions.
• Methods declared as future aren’t allowed in classes that implement the Database.Batchable interface.
• Methods declared as future can’t be called from a batch Apex class.
• All methods in the class must be defined as global or public.

References

·         https://developer.salesforce.com/docs/atlas.en-us.apexcode.meta/apexcode/apex_batch_interface.htm