Batch Job

Enhanced Definition

A batch job on z/OS is a non-interactive program or series of programs executed sequentially without direct user intervention. It is typically submitted to the system for processing in a queue and runs to completion, often processing large volumes of data.

Key Characteristics

- Non-interactive Execution: Runs autonomously without requiring real-time input or interaction from a human operator during its execution.
- JCL-driven: Defined and controlled by Job Control Language (JCL) statements, which specify the programs to execute, data sets to use, and execution parameters.
- Asynchronous Processing: Submitted to the Job Entry Subsystem (JES) and queued for execution, running when system resources become available, independent of the submission time.
- Resource Consumption: Can be significant, often requiring dedicated CPU time, memory (REGION), and I/O resources, especially for large-scale data processing tasks.
- Output Management: Generates output (e.g., reports, log files, updated data sets) that is typically spooled by JES and can be viewed, printed, or archived.
- Return Code Based: The success or failure of individual job steps and the overall job is indicated by return codes, which can be used for conditional processing.

Use Cases

- End-of-Day/Month Processing: Running financial reconciliations, billing cycles, payroll processing, or inventory updates that involve large transactional data sets.
- Data Transformation and Loading (ETL): Extracting data from various sources, transforming it according to business rules, and loading it into databases (e.g., DB2, IMS) or files.
- Report Generation: Producing daily, weekly, or monthly reports from operational data for business analysis, auditing, and compliance purposes.
- System Utilities and Maintenance: Executing utility programs for data set management, backup and recovery, data migration, or system health checks.
- Application Compilations: Compiling COBOL, PL/I, or Assembler programs and linking them into executable load modules for deployment.

Related Concepts

Batch jobs are fundamental to z/OS operations, relying heavily on JCL to define their execution environment and steps. The Job Entry Subsystem (JES) (JES2 or JES3) manages the submission, scheduling, execution, and output of batch jobs. They often execute COBOL or PL/I application programs, interact with DB2 or IMS databases, and process data stored in VSAM or sequential data sets. They contrast with online transactions (e.g., CICS transactions) which are interactive and typically process smaller units of work.

Best Practices:

Optimize JCL: Ensure JCL is efficient, using appropriate DD statements, DISP parameters, and REGION specifications to minimize resource contention and improve throughput.
Implement Robust Error Handling: Utilize COND parameters in JCL and RETURN-CODE checks within programs to manage job step dependencies and gracefully handle expected and unexpected errors.
Monitor Performance: Regularly review job logs, CPU usage, I/O statistics, and elapsed times to identify bottlenecks and optimize long-running or resource-intensive jobs.
Version Control: Store JCL and program source code in a version control system to track changes, facilitate rollbacks, and ensure consistency across environments.
Automate Scheduling: Leverage job schedulers (e.g., IBM Z Workload Scheduler, CA 7, Control-M) to automate the submission, dependency management, and restart capabilities of complex batch streams.