Demand - Immediate requirement

Enhanced Definition

In the mainframe context, "demand - immediate requirement" refers to a critical need for rapid processing, resource allocation, or system response that must be met without significant delay. This typically applies to high-priority transactions, time-sensitive batch jobs, or urgent system events that directly impact business operations or user experience. In the mainframe context, an "immediate requirement" refers to a task, transaction, or operation that demands real-time processing and a rapid response, typically within milliseconds or seconds. These are critical, often interactive, requests that cannot tolerate significant delays and are central to online transaction processing (OLTP) and responsive system management on z/OS.

Key Characteristics

- Low Latency Expectation: Implies a requirement for minimal response time, often measured in milliseconds or sub-seconds for online transactions.
- High Priority: Workloads meeting an immediate requirement are typically assigned higher dispatching priorities by z/OS Workload Manager (WLM) to ensure preferential access to system resources.
- Resource Intensive (Potentially): May necessitate immediate and exclusive access to CPU cycles, I/O channels, memory, or specific data resources.
- Event-Driven: Often triggered by external user interactions (e.g., CICS transactions), critical system alerts, or time-sensitive business events.
- Synchronous Processing: Many immediate requirements involve synchronous interactions where the requesting entity awaits an immediate response.

Use Cases

- Online Transaction Processing (OLTP): CICS or IMS TM transactions, such as ATM withdrawals, credit card authorizations, or real-time inventory lookups, where sub-second response times are crucial.
- Critical Batch Job Execution: A JCL job stream for end-of-day financial settlement or urgent data synchronization that must complete within a strict time window.
- Real-time Data Updates: Immediate updates to DB2 or IMS DB databases reflecting critical business events, like booking a flight or processing an order.
- System Monitoring and Alerts: z/OS console messages or SMF records indicating a critical system condition (e.g., storage shortage, device error) that requires immediate operator or automated intervention.

Related Concepts

Meeting immediate requirements is central to Workload Manager (WLM), which dynamically adjusts resource allocation to ensure performance goals for critical workloads are met. It is fundamental to Online Transaction Processing (OLTP) systems like CICS and IMS TM, where responsiveness directly impacts business continuity. Furthermore, it influences Job Entry Subsystem (JES) scheduling and dispatching priorities for batch processing and drives the need for robust high availability and disaster recovery strategies to ensure continuous service for these critical demands.

Best Practices:

WLM Goal Definition: Clearly define WLM performance goals for workloads identified as "immediate requirements" to ensure they receive appropriate priority and resources.
Efficient Application Design: Develop COBOL or Assembler applications with optimized code paths, minimal I/O operations, and efficient resource utilization to reduce processing time for critical transactions.
Resource Provisioning: Ensure adequate CPU, memory, and I/O capacity is provisioned to handle peak loads for immediate requirements without contention.
Proactive Monitoring: Implement comprehensive SMF and RMF monitoring with automated alerts for performance degradation, resource bottlenecks, or system events that could impact immediate requirements.
Transaction Atomicity: Design CICS or IMS transactions to be short-lived and atomic, minimizing database lock durations and improving concurrency for other demanding workloads.