Job Stream

Enhanced Definition

A job stream, often referred to as a job flow or batch stream, is a predefined sequence of two or more `jobs` that are executed in a specific order on an IBM z/OS mainframe. Its primary purpose is to automate a series of related tasks, where the output of one job often serves as the input for a subsequent job within the same stream.

Key Characteristics

- Sequential Execution: Jobs within a stream are typically processed one after another, adhering to a predefined order.
- Inter-Job Dependencies: Successive jobs often have data or logical dependencies, meaning a later job might require the successful completion or output of an earlier job.
- Batch Processing Focus: Job streams are fundamental to batch processing, handling high volumes of data processing, reporting, and system maintenance tasks.
- Automation via Schedulers: While JCL defines individual jobs, workload automation products (like IBM Workload Scheduler for z/OS (TWS/OPC) or Broadcom CA-7) manage the execution, dependencies, and scheduling of complex job streams.
- Error Propagation: A failure in an early job within a stream can prevent subsequent dependent jobs from running, often requiring manual intervention or automated restart procedures.

Use Cases

- Daily Batch Cycle: Processing end-of-day transactions, updating master files, generating financial reports, and performing data backups as part of a nightly or daily operational cycle.
- Database Maintenance and Utilities: A stream might include jobs to unload DB2 tables, reorganize them, rebuild indexes, and then reload the data, ensuring optimal database performance.
- Application Deployment: Compiling COBOL programs, linking them into load modules, and then deploying them to production libraries can be automated as a job stream.
- Data ETL (Extract, Transform, Load): Extracting data from various sources (e.g., VSAM files, IMS databases), transforming it using COBOL or utility programs, and loading it into a data warehouse or another application's datasets.

Related Concepts

A job stream is fundamentally built upon individual jobs, each defined by JCL (Job Control Language) that specifies the programs to run and the resources to use. Workload schedulers are crucial for managing and automating job streams, handling complex dependencies, conditional execution, and restart capabilities. Jobs within a stream frequently interact by passing data through datasets (e.g., sequential files, GDGs) or by updating shared resources like DB2 tables or IMS databases.

Best Practices:

Modularity and Simplicity: Design individual jobs within a stream to perform a single, well-defined logical function to improve maintainability and error isolation.
Robust Error Handling: Implement JCL conditional processing (COND=) and program logic to gracefully handle expected errors, log failures, and facilitate restarts.
Clear Documentation: Document the purpose of the job stream, the function of each job, inter-job dependencies, expected inputs/outputs, and restart procedures.
Parameterization: Utilize JCL symbolic parameters (SET statements or PROC parameters) to make job streams flexible and reusable across different environments or processing cycles.
Monitoring and Alerting: Leverage workload automation tools to monitor job stream progress, set up alerts for failures, and provide operators with clear restart instructions.