In this section, we will delve into the concepts of Restart and Checkpoint in JCL. These features are crucial for managing long-running jobs and ensuring that they can be restarted from a specific point in case of failure, rather than starting over from the beginning.

1. Restart: The ability to restart a job from a specific step or point after a failure.
2. Checkpoint: A mechanism to save the state of a job at certain intervals, allowing it to be restarted from the last saved state.

• Efficiency: Reduces the need to rerun entire jobs, saving time and resources.
• Reliability: Ensures that jobs can recover from failures without losing significant progress.
• Resource Management: Helps in managing system resources more effectively by avoiding redundant processing.

The RESTART parameter is used in the JOB statement to specify the step from which the job should be restarted.

Syntax:

Example:

In this example, if the job fails at STEP3, it can be restarted from STEP2 using the RESTART=STEP2 parameter.

Checkpoints are typically used in conjunction with application programs that support checkpoint/restart logic. The application program must be designed to take checkpoints and restart from them.

Example:

In this example, PROG1 is designed to take checkpoints. If the job fails, it can be restarted from the last checkpoint taken by PROG1.

The RD (Restart Definition) parameter in the JOB statement can be used to specify automatic restart options.

Syntax:

Example:

In this example, the RD=R parameter indicates that the job should be automatically restarted from the point of failure.

Let's consider a practical example where a job takes checkpoints and can be restarted from the last checkpoint.

JCL Code:

Explanation:

1. STEP1 runs PROG1 with a parameter indicating that it should take checkpoints.
2. If the job fails at STEP3, it can be restarted from STEP2 using the RESTART=STEP2 parameter.
3. PROG1 will use the last checkpoint to resume processing, ensuring that no work is lost.

Task: Write a JCL job that includes three steps. The first step should take checkpoints, and the job should be restartable from the second step.

Solution:

Explanation:

• STEP1 runs PROG1 with checkpointing enabled.
• The job can be restarted from STEP2 if it fails, ensuring that PROG1 resumes from the last checkpoint.

• Incorrect Step Name: Ensure that the step name specified in the RESTART parameter matches exactly with the step name in the job.
• Checkpoint Logic: Make sure that the application program supports checkpoint/restart logic and is correctly configured to take checkpoints.
• Resource Management: Be mindful of resource allocation when using checkpoints, as they can consume additional system resources.

In this section, we covered the concepts of Restart and Checkpoint in JCL, their importance, and how to implement them. By using these features, you can make your JCL jobs more efficient and reliable, ensuring that they can recover from failures without losing significant progress. In the next section, we will explore common JCL errors and how to interpret error messages.