Apex Batch

What is Asynchronous Process ?

Asynchronous process means that a process operating independently of other processes.An Asynchrounous process executes a task in the background.User does not have to wait for the task to finish

User Asynchronous Apex for :

1) Callouts to external Systems2) Operations that require higher limits3) Code that needs to run at a certain time
Asynchronous apex can be implemented using different techniques which include Future Methods,Batch Apex, Queueable Apex and Scheduled Apex.

Key benefits of Asynchronous Apex in Salesforce :

User Efficiency
Scalability
Higher Governor Limites

We have the following types of asynchronous apex:

Future methods
Queueable Apex
Batch Apex
Scheduled Apex

What is Future method in Salesforce ?

A Future runs as asynchronously. you can call future method for executing long-running operations, such as callout to external Web services or any operation you would like to run in its own thread, on its own time. Each Future method is queued and executes when system resources become available. That way the execution of your code doesn't have to wait for the completion of a long-running operation.

Future method Syntax :

global class MyClass{

@future

public static void myFutureMethod(){

// Perform some operations

}

Future Method Considerations :

1) Methods with the future annotation must be static methods 2) Can only return a void type 3) The specified parameters must be primitive data types, arrays of primitive data types, or collections of primitive data types 4) Methods with the future annotation can not take sObjects or objects as arguments 5) You can invoke future methods the same way you invoke any other method. However, a future method can not invoke another future method 6) No more than 50 method call per Apex invocation

What is the Queueable Apex?

Queueable Apex is another asynchronous type of apex. It runs in a separate thread and executes whenever the resources are available. In this type, we can queue our jobs and it is used to run long-running operations. Here we can get the job Id to monitor our jobs.

Syntax :

public class UpdateAccountsJob implements Queueable {

public void execute(QueueableContext context) {

List<Account> accounts = [SELECT Id, Name FROM Account WHERE Industry = 'Technology'];

for (Account acc : accounts) {

acc.Industry = 'Updated Industry';

}

update accounts;

}

// To run it:

System.enqueueJob(new UpdateAccountsJob());

Here are some key features of Queueable Class:

1) A class and method that can be added to the queue to be executed.2) It’s monitorable and abortable.3) It’s chain able.4) A public class that implements the Queueable interface5) Includes an execute method that accepts only a Queueable Context parameter.6) The execute method can access instance properties for the class.7) Returns void.8) Launch by calling System.enqueueJob(cls) with an instance of the class.9) Returns an AsyncApexJob Id

What is Batch Apex in Salesforce

Batch Apex is used to process at large set of data. That executes every transaction, by breaking down large sets of data into small chunks and providing us with the additional benefit of a governor limits.Every batch in the Batch Apex runs with the new set of governor limits. in other words the governor limit will reset for every batch that is executing.So. we can use Batch Jobs for Operations like Data deletion, mass Update etc.

Database.Batchable interface Methods :

Start method – identifies the scope (list of data to be processed) Execute method – processes a subset of the scoped records Finish method – does any post-job wrap-up

Additional interfaces:

1. Database.Stateful
2. Database.AllowsCallouts

Some key points for batch job in Salesforce

Launch by calling Database.executeBatch(cls) with an instance of the class and an optional scope size
Default scope size is 200
Max scope size is 2,000
Returns an AsyncApexJobId

How to use Batch Apex?

Batch Apex, we have to implement the salesforce provided interface Database.Batchable.Database.Batchable Interface has three methods that we have to implement :

1. Start
2. Execute
3. Finish

Every method in the Database.Batchable Interface wwll require a reference to Database.BatchableContext.

Start Method :

        In this method, we collect the records of objects either with a Database.QueryLocator or iterable to pass them into execute method for operating.
       Syntax :       public Database.QueryLocator start(Database.BatchableContex BC){        // Code here..               }

Execute Method :            The start method will collect data and pass it into the Execute, wich will break it into chunks.            This method will run multiple times according to the Batch size provided.           It takes ad additional parameter, which will be the list of object data we have collected in the start method.
        Syntax :        public void execute(Database.BatchableContext BC, List<P>){            // code here..        }
Finish method :            This method will run after processing al lthe batches, However, we can use this to perform any post activities or send confirmation emails                 Syntax :        public void finish(Database.BatchableContext BC){       // Code here..          }

How to Execute the Batch ?

To execute the Batch we have to create the instance first, of out Batch ClassLike (UpdateContactField) then execute it by using Database.executeBatch.

Example :

UpdateContactFields batchObj = new UpdateContactFields(); Database.executeBatch(batchObj);

Node :

The default batch size is 200 and maximum batch size is 2000. We can also specify the batch size at the time of execution. If we don't specify then batch will be executed with the default size.

There are following Batch job Status :

1) Holding :

The job has been submitted and waiting for the resources to queue the job.

2) Queued :

Execution is pending.

3) Preparing :

After the execution of the start method, the status will last for a few minutes, depending on the size of the records.

4) Processing :

Execution has started.

5) Aborted :

If we abort the job menually then this status will get updated.

6) Completed :

If the job is completed whether with or without fail

7) Failures :

If the job went int some system failure. (Any overner limit or any other limitations.

What are the limitations of Batch Apex ?

Database.QueryLocator can return up to 50 million records, if itpasses more than 50 million, then it terminates and marks the job as a failure.
We can queue a mazimum of 5 jobs or in other words 5 obj can be active at the same time.
The maximum batch size 2000 so if we pass mre than that it will break into smaller chunks.
The org can run only one Batch job's start method at the same time

What are the best practices for Batch Apex ?

The implementation method of the Database.Batchable interface must be dfined as public or global.
If more than 2000 request are in the queue, other request will be delayed. As a best practice try to reduce the batch size.
Furthermore , avoid using related subqueries, as they can slow down the execution speed of the batch.
Also, the Batch class can't call the method declared with a future annotation.
Batch Apex job perform more efficiently when the start method generates a QueryLocator object without incorporating related records using subqueries.

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