Asynchronous Apex

Future, Queueable, Batch and Schedulable Apex — when to use each, with examples and limits.

Developer 2 min readAsyncFutureQueueableBatchSchedulable

Async Apex runs later, in its own transaction, with higher limits (200 SOQL, 60 s CPU, 12 MB heap).

Comparison

	`@future`	Queueable	Batch	Schedulable
Start	Call the method	`System.enqueueJob(job)`	`Database.executeBatch(job, size)`	`System.schedule(name, cron, job)`
Parameters	Primitives / collections of primitives only	Any (sObjects, objects)	Query or Iterable	—
Job Id / monitoring	❌	✅ `AsyncApexJob`	✅	✅ `CronTrigger`
Chaining	❌	✅ enqueue from `execute`	✅ start another in `finish`	Launches other jobs
Best for	Simple fire-and-forget, callouts from triggers	Most async work	Millions of records	Time-based runs

@future

apex

public class GeoService {
    @future(callout=true)
    public static void geocode(Set<Id> accountIds) {
        // callout + update; can't take sObjects as parameters
    }
}

Queueable

apex

public class SyncContactsJob implements Queueable, Database.AllowsCallouts {
    private List<Contact> contacts;
    public SyncContactsJob(List<Contact> contacts) { this.contacts = contacts; }

    public void execute(QueueableContext ctx) {
        // work with complex types, then optionally chain:
        // System.enqueueJob(new NextJob());
    }
}

Id jobId = System.enqueueJob(new SyncContactsJob(newContacts));

Batch Apex

apex

public class DeactivateStaleAccounts implements Database.Batchable<SObject>, Database.Stateful {
    private Integer processed = 0;

    public Database.QueryLocator start(Database.BatchableContext bc) {
        return Database.getQueryLocator(
            'SELECT Id FROM Account WHERE LastActivityDate < LAST_N_DAYS:365'
        );
    }
    public void execute(Database.BatchableContext bc, List<Account> scope) {
        for (Account a : scope) a.Active__c = 'No';
        update scope;
        processed += scope.size();
    }
    public void finish(Database.BatchableContext bc) {
        System.debug('Deactivated ' + processed + ' accounts');
    }
}

Database.executeBatch(new DeactivateStaleAccounts(), 200);  // scope 1–2,000

QueryLocator can process up to 50 million records.
Each execute call is its own transaction with fresh limits.
Database.Stateful keeps instance variables between chunks.

Schedulable

apex

public class NightlyCleanup implements Schedulable {
    public void execute(SchedulableContext sc) {
        Database.executeBatch(new DeactivateStaleAccounts());
    }
}
// Every day at 2 AM:
System.schedule('Nightly cleanup', '0 0 2 * * ?', new NightlyCleanup());

Testing async code

apex

Test.startTest();
System.enqueueJob(new SyncContactsJob(cons));
Test.stopTest();   // async work runs synchronously here, then assert

Interview questions

Why can't @future methods take sObjects? → The record may change before the method runs; pass Ids and re-query.
Queueable vs Future? → Queueable: complex params, job Id, chaining.
How many records can batch Apex process? → Up to 50 million with a QueryLocator.
How do you test async Apex? → Wrap in Test.startTest() / Test.stopTest().

Order of Execution

Apex Testing