Job chaining and batching in Laravel - Step-by-Step Execution

Concept Flow - Job chaining and batching

Create Jobs

↓

Chain Jobs?

Yes→Set chain order

↓

Dispatch chained jobs

↓

Batch Jobs?

Yes→Create batch

↓

Dispatch batch

↓

Dispatch single job

↓

Job(s) execute in order or parallel

↓

Jobs complete with success/failure callbacks

This flow shows how Laravel creates jobs, optionally chains or batches them, dispatches, and then executes with callbacks.

Execution Sample

Laravel

use App\Jobs\Job1;
use App\Jobs\Job2;

Job1::withChain([new Job2()])->dispatch();

This code dispatches Job1 and chains Job2 to run after Job1 finishes.

Execution Table

Step	Action	Jobs Created	Chain Set	Batch Created	Dispatch Action	Job Execution Order	Callback Triggered
1	Create Job1 instance	Job1	No	No	No	None	No
2	Create Job2 instance for chain	Job1, Job2	Yes (Job2 after Job1)	No	No	None	No
3	Dispatch Job1 with chain	Job1, Job2	Yes	No	Job1 dispatched	Job1 first	No
4	Job1 executes	Job1, Job2	Yes	No	Job1 running	Job1 running	No
5	Job1 completes successfully	Job1, Job2	Yes	No	Job1 done	Job1 done	No
6	Job2 dispatched automatically after Job1	Job1, Job2	Yes	No	Job2 dispatched	Job2 next	No
7	Job2 executes	Job1, Job2	Yes	No	Job2 running	Job2 running	No
8	Job2 completes successfully	Job1, Job2	Yes	No	Job2 done	Job2 done	Success callback triggered
9	All chained jobs done	Job1, Job2	Yes	No	No	All done	Chain complete callback triggered
10	Exit	Job1, Job2	Yes	No	No	All done	All callbacks done

💡 All chained jobs executed in order; callbacks triggered after completion.

Variable Tracker

Variable	Start	After Step 2	After Step 3	After Step 6	After Step 9
Jobs Created	None	Job1, Job2	Job1, Job2	Job1, Job2	Job1, Job2
Chain Set	No	Yes (Job2 after Job1)	Yes	Yes	Yes
Batch Created	No	No	No	No	No
Dispatch Action	No	No	Job1 dispatched	Job2 dispatched	No
Job Execution Order	None	None	Job1 first	Job2 next	All done
Callback Triggered	No	No	No	No	Chain complete callback

Key Moments - 3 Insights

Why does Job2 only start after Job1 finishes?

Because the chain sets Job2 to run only after Job1 completes successfully, as shown in execution_table step 6 where Job2 dispatch happens after Job1 done.

What happens if a job in the chain fails?

The chain stops executing further jobs and failure callbacks run. This is implied by the chain behavior in the execution_table where jobs run sequentially and callbacks trigger on success or failure.

How is batching different from chaining?

Batching runs multiple jobs in parallel as a group, while chaining runs jobs one after another. Our example shows chaining with no batch created (Batch Created stays 'No').

Visual Quiz - 3 Questions

Look at the execution_table at step 4. What is the job execution order?

A Job1 is running

B Job2 is running

C Both Job1 and Job2 running in parallel

D No job running

💡 Hint

Check the 'Job Execution Order' column at step 4 in the execution_table.

At which step does Job2 get dispatched automatically?

A Step 3

B Step 6

C Step 5

D Step 7

💡 Hint

Look for 'Job2 dispatched' in the 'Dispatch Action' column in the execution_table.

If we added a batch instead of a chain, which variable would change in variable_tracker?

A Chain Set

B Jobs Created

C Batch Created

D Callback Triggered

💡 Hint

Check the 'Batch Created' row in variable_tracker to see when batches are created.

Concept Snapshot

Laravel Job Chaining & Batching:
- Chain jobs to run one after another using withChain()
- Batch jobs to run many in parallel using Bus::batch()
- Dispatch chains or batches to queue
- Callbacks run on success or failure
- Chains run sequentially; batches run concurrently

Full Transcript

In Laravel, you create jobs to do tasks. You can chain jobs so one runs after another finishes, or batch jobs to run many at once. When you chain jobs, Laravel waits for the first job to finish before starting the next. If a job fails, the chain stops. Batching runs jobs in parallel and lets you track progress. This example shows creating two jobs, chaining them, dispatching the first, then the second runs automatically after the first completes. Callbacks run after all jobs finish. This helps organize complex tasks in order or groups.

Practice

1. What is the main difference between job chaining and job batching in Laravel?

easy

A. Job chaining is for database tasks only; job batching is for email tasks only.

B. Job chaining runs jobs in parallel; job batching runs jobs sequentially.

C. Job chaining runs jobs one after another; job batching runs jobs together and tracks progress.

D. Job chaining requires manual tracking; job batching does not track progress.

Solution

1. Step 1: Understand job chaining

   Job chaining runs jobs one after another in a specific order.

2. Step 2: Understand job batching

   Job batching runs many jobs together and tracks their progress as a group.

3. Final Answer:

   Job chaining runs jobs one after another; job batching runs jobs together and tracks progress. -> Option C

4. Quick Check:

   Job chaining = sequential, Job batching = grouped with progress [OK]

Hint: Chaining = sequence; batching = group with progress tracking [OK]

Common Mistakes:

• Confusing parallel and sequential execution
• Thinking batching runs jobs one by one
• Assuming chaining tracks progress automatically

2. Which of the following is the correct syntax to chain two jobs JobA and JobB in Laravel?

easy

A. JobA::chain([new JobB])->dispatch();

B. JobA::dispatch()->chain([JobB]);

C. dispatch(new JobA)->chain(new JobB);

D. dispatch(new JobA)->chain([new JobB]);

Solution

1. Step 1: Recall chaining syntax

   In Laravel, chaining jobs uses dispatch(new JobA)->chain([new JobB]).

2. Step 2: Check options for correct method calls

   dispatch(new JobA)->chain([new JobB]); matches the correct syntax with dispatch(new JobA)->chain([new JobB]);.

3. Final Answer:

   dispatch(new JobA)->chain([new JobB]); -> Option D

4. Quick Check:

   dispatch + chain array = correct chaining syntax [OK]

Hint: Use dispatch(new Job)->chain([jobs]) for chaining [OK]

Common Mistakes:

• Calling chain() on the job class instead of dispatch
• Passing a single job without array to chain()
• Using incorrect method order

3. Given the following code, what will be the output in the logs if all jobs succeed?

Bus::batch([
    new Job1(),
    new Job2(),
    new Job3()
])->then(function () {
    Log::info('Batch completed successfully');
})->dispatch();

medium

A. Logs 'Batch completed successfully' immediately after dispatch.

B. Logs 'Batch completed successfully' after all jobs finish.

C. No logs will be created because then() is not supported.

D. Logs 'Batch failed' if any job fails.

Solution

1. Step 1: Understand batch then() callback

   The then() callback runs after all jobs in the batch succeed.

2. Step 2: Analyze the code behavior

   Since all jobs succeed, the callback logs 'Batch completed successfully' after finishing.

3. Final Answer:

   Logs 'Batch completed successfully' after all jobs finish. -> Option B

4. Quick Check:

   Batch then() runs after success [OK]

Hint: then() runs after all batch jobs succeed [OK]

Common Mistakes:

• Thinking then() runs immediately after dispatch
• Assuming then() runs on failure
• Believing no logs are created

4. Identify the error in this job chaining code:

dispatch(new JobA)->chain(new JobB);

medium

A. chain() expects an array of jobs, not a single job instance.

B. dispatch() cannot be used with chaining.

C. JobB must be dispatched separately before chaining.

D. JobA must be a queued job class, not a job instance.

Solution

1. Step 1: Check chain() parameter requirements

   The chain() method requires an array of job instances.

2. Step 2: Analyze the code

   The code passes a single job instance new JobB without wrapping it in an array.

3. Final Answer:

   chain() expects an array of jobs, not a single job instance. -> Option A

4. Quick Check:

   chain() needs array of jobs [OK]

Hint: Always pass an array to chain(), even for one job [OK]

Common Mistakes:

• Passing a single job without array to chain()
• Trying to dispatch chained jobs separately
• Confusing dispatch and chain usage

5. You want to run three jobs JobX, JobY, and JobZ where JobY should only run after JobX completes, but JobZ can run anytime in parallel. Which Laravel approach correctly handles this?

hard

A. Use job chaining for JobX and JobY, and dispatch JobZ separately.

B. Use job batching for all three jobs together.

C. Chain JobX, JobY, and JobZ in one chain to run sequentially.

D. Dispatch all three jobs separately without chaining or batching.

Solution

1. Step 1: Understand job dependencies

   JobY depends on JobX finishing first, so they must run sequentially.

2. Step 2: Consider JobZ's independence

   JobZ can run anytime, so it should run separately in parallel.

3. Step 3: Choose correct Laravel approach

   Use chaining for JobX and JobY, and dispatch JobZ separately to run in parallel.

4. Final Answer:

   Use job chaining for JobX and JobY, and dispatch JobZ separately. -> Option A

5. Quick Check:

   Chain dependent jobs, dispatch independent jobs separately [OK]

Hint: Chain dependent jobs; dispatch independent jobs separately [OK]

Common Mistakes:

• Batching all jobs when order matters only for some
• Chaining all jobs forcing sequential run
• Ignoring job dependencies