Workload Management

Job Entry Subsystems (JES) are z/OS components that manage job input, execution, and output processing. The two main JES implementations are:

• **JES2**: The primary JES for most z/OS installations, providing comprehensive job management, spool management, and network job entry capabilities
• **JES3**: Designed for large, complex installations requiring advanced workload balancing and cross-system job management

JES subsystems receive jobs from various sources (terminals, networks, internal readers), manage job queues, allocate system resources, and handle job output. JES2 is more commonly used and provides features like job scheduling, dependency management, and workload balancing across multiple processors in a sysplex.

Job Control Language (JCL) is the scripting language used to define and control batch jobs on z/OS. JCL statements describe:

• **JOB statement**: Identifies the job and specifies accounting and execution parameters
• **EXEC statement**: Identifies the program to execute and its runtime parameters
• **DD (Data Definition) statements**: Define input/output data sets and their characteristics

JCL is crucial because it provides a standardized way to:
• Specify job requirements (CPU time, memory, special devices)
• Define data set allocations and dispositions
• Control job flow and error handling
• Ensure reproducible job execution

While JCL has a reputation for complexity, modern tools and utilities have made it more manageable, and it remains essential for batch processing on mainframe systems.

Batch processing on z/OS involves executing programs without user interaction, typically for large-scale data processing, report generation, and system maintenance. The batch processing workflow includes:

1. **Job submission**: Jobs are submitted via JCL to JES
2. **Job scheduling**: JES evaluates job requirements and system resources
3. **Resource allocation**: Initiators allocate required resources (CPU, memory, I/O)
4. **Job execution**: Programs run in dedicated address spaces
5. **Output processing**: Results are spooled and made available to users

Batch jobs can be simple single-step programs or complex multi-step processes with conditional execution. Modern z/OS supports both traditional batch workloads and integration with distributed systems through WebSphere Application Server and other middleware.

Job scheduling on z/OS is managed through JES and the Workload Manager (WLM), which determine when and where jobs execute based on:

• **Job classes**: Define execution priorities and resource limits
• **Initiators**: Dedicated address spaces that execute jobs
• **Job queues**: Hold jobs waiting for execution
• **Scheduling algorithms**: Consider job priority, resource availability, and system goals

Advanced scheduling features include:
• **Dependency management**: Jobs can wait for other jobs or resources
• **Time scheduling**: Jobs can be scheduled for specific times
• **Workload balancing**: Jobs can be routed across systems in a sysplex
• **Dynamic scheduling**: Adjusts based on current system conditions

The Workload Manager provides policy-based automation, ensuring critical workloads get priority while maintaining overall system performance.

Job classes and initiators are key components of z/OS workload management:

• **Job Classes**: Logical groupings that define job execution characteristics including:
- Priority levels (A highest, Z lowest)
- Resource limits (CPU time, memory)
- Execution windows
- Output handling

• **Initiators**: Special address spaces that execute batch jobs. Each initiator:
- Processes one job at a time
- Is associated with specific job classes
- Manages job execution resources
- Handles job completion and cleanup

The number of initiators and their class assignments determine how many jobs can run simultaneously and which types of jobs get priority. This architecture allows fine-grained control over workload distribution and ensures critical jobs receive appropriate resources.

Workload automation refers to the automated scheduling and management of IT processes across the enterprise. On z/OS, this includes:

• **Job scheduling**: Automated submission of batch jobs based on time, events, or dependencies
• **Dependency management**: Jobs waiting for completion of other jobs or external events
• **Workload balancing**: Distribution of work across multiple systems
• **Event-driven automation**: Triggering jobs based on system events or external conditions
• **Service level management**: Ensuring workloads meet performance objectives

IBM provides tools like Tivoli Workload Scheduler and Control-M for enterprise-wide workload automation. The z/OS Workload Manager (WLM) provides the foundation for workload automation by managing system resources and ensuring service level objectives are met.

A sysplex (systems complex) is a cluster of z/OS systems that work together as a single logical system, providing enhanced workload management capabilities:

• **Workload balancing**: Jobs can be automatically routed to the least busy system
• **Resource sharing**: Shared access to data and resources across systems
• **High availability**: Work can continue if one system fails
• **Scalability**: Capacity can be added without disrupting operations

Sysplex workload management is handled by:
• **Coupling Facility**: Provides high-speed communication and shared memory
• **Workload Manager (WLM)**: Distributes work based on policies and goals
• **Cross-system services**: Enable resource sharing and coordination

Sysplex technology allows organizations to achieve higher availability, better resource utilization, and improved workload management across multiple z/OS systems.