Here's All you need to Know About Asynchronous Apex in Salesforce

Apex offers multiple ways to run your Apex code asynchronously. This can save you time and help you keep your code more organized.

Asynchronous apex is used to run process in a separate thread at later time.

It is a process or function that executes a test in the background without the user having to wait for the task to finish.

Benefits of Asynchronous Apex

Asynchronous apex comes with four different types. Depending on the use case, the user can identify which type suits the requirements

Future apex is used to run the process in a separate thread at a later time when system resources become available.

Methods are annotated with @future annotation.
It uses for calls out to external web services.
Operation you want to run in their own thread.
Isolating DML operation on different sObjects type to prevent the mixed DML error.

Must be static.
Only return a void type.
A parameter must be a primitive data type.
An array of primitive data types.
Don't take standard or custom object as argument.
Common pattern is to pass the method a list of record Ids that you want to process asynchronously.

Batch Apex in Salesforce is an important tool used to process large amounts of records without exceeding normal platform limits.

To use batch Apex, write an Apex class that implements the Salesforce-provided interface Database.Batchable and then invoke the class programmatically.
Execute codes in small batches at a time
Batch apex is monitorable and abortable
Batch Class always be global

Every batch class must have three methods

The Start and Finish method only executes once

Execute method executes equal to the number of batches

A class and method that can be added to the queue to be executed
Queueable Class is monitorable and abortable.
Queueable Class is launched by calling System.Enqueue job(cls) With an instance of the class
It returns an async apex Job ID
Queueable Class is chainable
The difference between Queueable Apex and Future methods is –
Queueable Apex supports job-chaining
It supports non-primitive data types like sObjects or custom objects.
Maximum 50 jobs can be added to the queue in a single transaction.
Only one child job can exist for each parent job.
There is no limit on the dept of the chained jobs.

Schedulable Class is a global class that implements this schedulable interface
It Includes an execute method
Can be scheduled by calling system. Schedule (‘job name’, cron exp., cls)
Return cron trigger ID
CAN also scheduled via Salesforce UI
When a class is scheduled, a CronTrigger object is created.
The getTriggerId method can be used to return the ID of a CronTrigger record.
If the class is scheduled from Trigger, the Governor limit should be checked.
The additional processing should be done in a separate class outside of the execution method.
You can have up to 100 scheduled Apex jobs at a time.

Type	Overview	Common Scenarios
Future Methods	Run in their own thread, and do not start until resources are available.	Web service callout.
Batch Apex	Run large jobs that would exceed normal processing limits.	Data cleansing or archiving of records.
Queueable Apex	Similar to future methods, but provide additional job chaining and allow more complex data types to be used.	Performing sequential processing operations with external Web services.
Scheduled Apex	Schedule Apex to run at a specified time.	Daily or weekly tasks.