Expedite

Enhanced Definition

In the mainframe context, "expedite" refers to the act of assigning a higher priority to a specific job, task, transaction, or process to ensure its faster execution and completion. This typically overrides normal scheduling or resource allocation, making it a critical mechanism for urgent or time-sensitive workloads.

Key Characteristics

- Priority Elevation: Involves increasing the dispatching or execution priority of a workload within the z/OS operating system or a specific subsystem (e.g., CICS, IMS).
- Resource Preference: Expedited tasks receive preferential access to CPU cycles, I/O resources, and memory, potentially at the expense of lower-priority workloads.
- System-wide Impact: Can affect overall system performance by diverting resources from other tasks, requiring careful management and monitoring.
- Dynamic or Pre-defined: Prioritization can be applied dynamically by an operator or system administrator, or pre-defined through workload management policies like z/OS Workload Manager (WLM) service classes.
- Subsystem Specific: Implementation details vary; for instance, CICS transactions have specific priority settings distinct from batch job priorities.

Use Cases

- Critical Batch Job Completion: Expediting a nightly batch job that failed and needs to be re-run immediately to meet a strict business deadline.
- High-Priority Online Transaction: Prioritizing a CICS transaction for a critical customer service application during peak hours to ensure rapid response times.
- System Recovery Tasks: Giving higher priority to system utilities or recovery processes after an outage to restore services quickly and minimize downtime.
- Ad-hoc Reporting: Expediting an urgent ad-hoc report generation required by management within a very short timeframe.
- Problem Diagnosis: Elevating the priority of diagnostic tools or tracing utilities to capture critical information during a production issue for faster resolution.

Related Concepts

Expediting is fundamentally linked to Workload Manager (WLM), which is responsible for managing system resources and dispatching tasks based on defined service goals and importance. It often involves manipulating dispatching priority or assigning a higher service class to a workload. It contrasts with standard job scheduling, where jobs typically run based on submission order and pre-defined, static priorities. In CICS, transaction priorities can be set to expedite critical online processes, while in JCL, the PRIORITY parameter can influence batch job execution priority.

Best Practices:

Judicious Use: Expedite sparingly and only for genuinely critical workloads, as overuse can degrade overall system performance and lead to resource contention for other important tasks.
Monitor Impact: Always monitor system performance (CPU utilization, I/O, response times) when expediting to understand its impact on other workloads and ensure it doesn't create new bottlenecks.
WLM Integration: Leverage z/OS Workload Manager (WLM) service classes and importance levels to manage and automate the prioritization of critical workloads, rather than relying solely on manual operator intervention.
Documentation: Document the procedures and criteria for when and how to expedite tasks, ensuring consistency, auditability, and preventing misuse.
Root Cause Analysis: For frequently expedited jobs, investigate the underlying reasons (e.g., inefficient code, poor design, inadequate resources) and address them through performance tuning or system upgrades, rather than using priority elevation as a permanent solution.