This document provides an overview of Force.com Batch Apex, which allows processing of large data sets asynchronously by splitting the data into batches that are processed sequentially. Key aspects covered include the batchable interface with start, execute, and finish methods; splitting data into transactions of up to 200 records each; monitoring and error handling; making batches stateful; using query locators or iterables; testing and scheduling batches; and limitations of batch apex.

1. Force.com Batch Apex
Sujit Kumar
Zenolocity LLC © 2012 - 2024

2. Overview
• Concepts
• Batchable Interface
• Guidelines
• Example Apex Batch Job
• Execution and Monitoring
• Stateful Batch Apex
• Iterable Batch
• Limitations
• Testing and Scheduling

3. Concepts
• Large, data-intensive processing.
• Scope: set of records Batch Apex works on. One to 50
million records. Scope is usually expressed as a SOQL
statement, which is contained in a Query Locator, a system
object that is exempt from the normal governor limits on
SOQL.
• Batch Job: Asynchronous, run in background. UI to list,
monitor and cancel batch jobs.
• Transactions: Units of work running the same code within a
batch job, subject to governor limits. Up to 200 records.
The scope is split into several transactions, each committed
to the database independently. Stateless. Parallel or serial.
• 5 Active Batch Jobs per Org.

4. Batchable Interface
• start() - return a QueryLocator or an Iterable that
describes the scope of the batch job.
• execute() – splits the records from the previous step
into several transactions, each of which operates on up
to 200 records.
• The records are provided in the scope argument of the
execute method.
• Each invocation of execute is a separate transaction.
• If an uncaught exception is in a transaction, no further
transactions are processed and the entire batch job is
stopped.

5. Transactions in Batch Job
• Transactions that complete successfully are never
rolled back.
• If an error in a transaction stops the batch, the
transactions executed up to that point remain in
the database.
• Cannot use savepoints to achieve a single
pseudo-transaction across the entire batch job.
• If you must achieve job-wide rollback, this can be
implemented in the form of a compensating
batch job that reverses the actions of the failed
job.

6. Batchable (contd…)
• finish() - Invoked once at the end of a batch
job.
• The job ends when all transactions in the
scope have been processed successfully, or if
processing has failed.
• Regardless of success or failure, finish is
always called.
• No code required in the finish method.

7. Batch Apex Class
• Must implement the Database.Batchable
interface. Parameterized interface, so needs a
type name. Use SObject for batches with a
QueryLocator scope, or any database object
type for an Iterable scope.
• The class must be global, hence methods must
be global as well.

8. Batchable Context
• The BatchableContext object argument in all
three methods contains a method called getJobId
to get unique ID of the current batch job.
• jobID can be used to look up additional
information about the batch job in the standard
database object AsyncApexJob.
• You can also pass this identifier to the
System.abortJob method to stop processing of
the batch job.

9. Guidelines
• Single DB Object – source data from a single
DB object, no web services,
• Simple scope of work – single SOQL typically.
• Minimal shared state – each unit of work is
independent.
• Limited transactionality – rollback requires
custom code.
• Not time critical – no guarantee on when it is
executed and how long it will run.

10. Running Batch Jobs
• 4 ways: execute from a VF page, schedule it or kick off
from a trigger or run it from the Execute Anonymous
view in the Force.com IDE.
• Execute from the Anonymous view.
HelloBatchApex batch = new HelloBatchApex();
Id jobId = Database.executeBatch(batch);
System.debug('Started Batch Apex job: ' + jobId);
Pass an extra argument to executeBatch to control the scope.

11. Job States
• Queued
• Processing
• Aborted
• Successful

12. 4 Different Logs in Debug Logs
• Results of evaluating the code in the Execute
Anonymous view.
• Invocation of the start method to prepare the
dataset for the batch.
• Results of running the execute method, where
the batch job performs its work on the subsets of
the data.
• All the transactions have been processed, so the
finish method is called to allow post-processing
to occur.

13. Stateful Batch
• Batch Apex is stateless by default. That means for
each run of the execute method, you receive a
fresh copy of your object. All fields of the class ,
both static and instance are initialized.
• If your batch process needs information that is
shared across transactions, one approach is to
make the Batch Apex class itself stateful by
implementing the Stateful interface.
• This instructs Force.com to preserve the values of
your static and instance variables between
transactions.

14. Compare QueryLocator and Iterable
Batch
Feature QueryLocator Iterable Batch
Number of Records 1 to 50 million Max of 50k records
How it works? Uses exactly 1 SOQL
without governor limits
Custom Apex Code, can
use complex criteria,
subject to governor limits.

15. Iterable Batch
• Global class that must implement 2 interfaces:
the Iterator interface and the Iterable interface.
• Iterator – hasNext() and next() global methods.
• Iterable – single global method called Iterator().
• You could write two separate classes, one to
implement each interface. Or you can implement
both interfaces in the same class.

16. Limitations of Apex Batch
• No future methods allowed.
• Run as system user, so have permission to read and
write all data in the org.
• Max heap size is 6MB.
• Exactly 1 callout to external systems allowed for each
invocation of start, execute and finish. Must implement
Database.AllowsCallouts interface.
• Reduce the default 200 records per transaction if
intensive work needs to be done that may exceed the
governor limits.
• Max number of queued or active jobs in an org is 5.

17. Testing Batch Apex
• Batch Apex can be tested like any Apex code, although
you are limited to a single transaction’s worth of data
(one invocation of the execute method).
• A batch job started within a test runs synchronously,
and does not count against the organization’s limit of 5
batch jobs.
public static testmethod void testBatch() {
Test.startTest();
HelloBatchApex batch = new HelloBatchApex();
ID jobId = Database.executeBatch(batch);
Test.stopTest();
}

18. Schedule Batch Apex
• Enables any Apex code, not just Batch Apex, to be
scheduled to run asynchronously at regular time intervals.
• An Apex class that can be scheduled by Force.com must
implement the Schedulable interface. Marker Interface =>
no methods.
• Code that is executed by the scheduler runs as the system
user, so sharing rules or other access controls are not
enforced.
• At most 10 classes can be scheduled at one time.
• Programmatic approach:
System.schedule('Scheduled Test', '0 0 1 * * ?',
new HelloSchedulable());

19. Create Scheduled Batch Job
global class HelloSchedulable
implements Schedulable {
global void execute(SchedulableContext sc)
{
HelloBatchApex batch = new
HelloBatchApex();
Database.executeBatch(batch);
}
}