Initiation

Enhanced Definition

In z/OS, "initiation" refers to the process by which the Job Entry Subsystem (JES) selects a submitted job from its input queue and prepares it for execution on a system's processor. It involves allocating necessary system resources, establishing the execution environment, and assigning an initiator (an address space) to manage the job's steps.

Key Characteristics

- Job Selection: JES (either JES2 or JES3) selects jobs based on criteria such as job class, priority, and resource availability, moving them from the input queue to the execution phase.
- Initiator Assignment: An "initiator" is a system-managed address space that is allocated to a job during initiation to control its execution from start to finish.
- Resource Allocation: The system allocates critical resources like memory (e.g., job pack area), datasets, and I/O devices required by the job's JCL.
- Environment Setup: A dedicated execution environment (address space) is created for the job, isolating it from other concurrent workloads.
- JCL Interpretation: The initiator begins interpreting the Job Control Language (JCL) statements, resolving symbolic parameters and preparing for the execution of the first job step.
- System-Controlled: This process is entirely managed by z/OS and JES, ensuring orderly and efficient processing of batch workloads.

Use Cases

- Batch Job Execution: When a COBOL application is submitted via JCL, initiation is the first step before the program's code begins to execute.
- Utility Program Runs: Running system utilities like IDCAMS, IEBGENER, or SORT requires job initiation to set up the environment for these programs.
- Started Tasks (STCs): While not typically queued through JES in the same way as batch jobs, the underlying process of starting and running a system service (like CICS, DB2, or an automation tool) involves a form of system initiation to allocate its address space and resources.
- Online Region Startup: The startup of critical online regions (e.g., CICS, IMS control regions) involves z/OS initiating these as started tasks, preparing their operational environment.

Related Concepts

Initiation is a crucial stage in the Job Entry Subsystem (JES) workflow, occurring after job submission and preceding job execution. It relies heavily on JCL to define the job's requirements and utilizes initiators (address spaces managed by JES) to prepare and manage the job's lifecycle. It is closely linked to Workload Manager (WLM), which influences job selection and initiator availability based on defined service goals, and resource management within z/OS.

Best Practices:

Optimize JCL: Ensure JCL is efficient, specifies correct resource requirements, and avoids unnecessary steps to streamline the initiation process.
Monitor Initiator Count: Regularly monitor the number of active initiators and adjust JES INIT parameters to match workload demands, preventing bottlenecks and ensuring timely job starts.
Effective Job Classing: Assign appropriate job classes and priorities to jobs to influence their selection during initiation, ensuring critical jobs are initiated promptly.
WLM Integration: Leverage WLM service definitions to manage initiator availability and job dispatching, allowing WLM to prioritize initiation based on business importance.
Pre-allocation of Resources: For critical jobs, consider pre-allocating frequently used datasets or resources where appropriate to reduce initiation time.

The term "Initiative - New effort" is a general business or project management concept and does not have a specific technical definition, implementation, or component within the IBM mainframe (z/OS, COBOL, JCL, CICS, DB2, IMS) ecosystem.

This glossary is specifically designed for technical terms relevant to mainframe and z/OS technologies, focusing on their technical characteristics, use cases, and relationships within that context. As "Initiative - New effort" is not a technical mainframe term, it does not fit the criteria for a glossary entry under the specified constraints.

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