Parallel processing in JCL allows multiple tasks to be executed simultaneously, improving the efficiency and performance of batch jobs. This section will cover the key concepts, practical examples, and exercises to help you understand and implement parallel processing in JCL.
Key Concepts
- Parallel Processing: The execution of multiple tasks or jobs at the same time to reduce overall processing time.
- Job Steps: Individual units of work within a JCL job that can be executed in parallel.
- Initiators: System resources that manage the execution of job steps. Multiple initiators allow for parallel processing.
- Dependencies: Conditions that determine the order of execution for job steps. Proper management of dependencies is crucial for successful parallel processing.
Practical Example
Example 1: Basic Parallel Processing
In this example, we will create a JCL job that runs two job steps in parallel.
//PARALLEL JOB (ACCOUNT),'PARALLEL PROCESSING EXAMPLE', // CLASS=A,MSGCLASS=A,NOTIFY=&SYSUID //STEP1 EXEC PGM=PROG1 //STEP2 EXEC PGM=PROG2
Explanation
- JOB Statement: Defines the job and its attributes.
- STEP1 and STEP2: Two job steps that will be executed in parallel. Each step runs a different program (
PROG1andPROG2).
Example 2: Parallel Processing with Dependencies
In this example, we will create a JCL job with three steps, where the third step depends on the completion of the first two steps.
//PARALLEL JOB (ACCOUNT),'PARALLEL PROCESSING WITH DEPENDENCIES', // CLASS=A,MSGCLASS=A,NOTIFY=&SYSUID //STEP1 EXEC PGM=PROG1 //STEP2 EXEC PGM=PROG2 //STEP3 EXEC PGM=PROG3,COND=(0,NE,STEP1),(0,NE,STEP2)
Explanation
- STEP3: This step will only execute if both
STEP1andSTEP2complete successfully (return code 0).
Exercises
Exercise 1: Create a Parallel Processing Job
Create a JCL job that runs three steps in parallel. Each step should execute a different program (PROG1, PROG2, and PROG3).
Solution
//PARALLEL JOB (ACCOUNT),'PARALLEL PROCESSING EXERCISE', // CLASS=A,MSGCLASS=A,NOTIFY=&SYSUID //STEP1 EXEC PGM=PROG1 //STEP2 EXEC PGM=PROG2 //STEP3 EXEC PGM=PROG3
Exercise 2: Parallel Processing with Conditional Execution
Create a JCL job with four steps. The fourth step should only execute if the first three steps complete successfully.
Solution
//PARALLEL JOB (ACCOUNT),'PARALLEL PROCESSING WITH CONDITIONAL EXECUTION', // CLASS=A,MSGCLASS=A,NOTIFY=&SYSUID //STEP1 EXEC PGM=PROG1 //STEP2 EXEC PGM=PROG2 //STEP3 EXEC PGM=PROG3 //STEP4 EXEC PGM=PROG4,COND=(0,NE,STEP1),(0,NE,STEP2),(0,NE,STEP3)
Common Mistakes and Tips
- Resource Contention: Ensure that parallel steps do not compete for the same resources, which can lead to contention and performance degradation.
- Proper Use of Initiators: Verify that your system has enough initiators to handle the parallel steps. Insufficient initiators can cause delays.
- Managing Dependencies: Clearly define dependencies to avoid race conditions and ensure correct execution order.
Conclusion
Parallel processing in JCL can significantly improve the performance of batch jobs by allowing multiple tasks to run simultaneously. By understanding the key concepts, practicing with examples, and being aware of common pitfalls, you can effectively implement parallel processing in your JCL jobs. In the next section, we will explore best practices for optimizing JCL jobs to further enhance performance.
JCL (Job Control Language) Course
Module 1: Introduction to JCL
Module 2: JCL Statements and Syntax
Module 3: Data Definition (DD) Statements
Module 4: Procedures and Symbolic Parameters
Module 5: Advanced JCL Concepts
- Conditional Processing
- JCLLIB and INCLUDE Statements
- Generation Data Groups (GDGs)
- Restart and Checkpoint
Module 6: Error Handling and Debugging
- Common JCL Errors
- Interpreting JCL Error Messages
- Debugging Techniques
- Using JES2/JES3 for Troubleshooting