Heuristic - Rule of thumb

Enhanced Definition

In the context of z/OS and mainframe computing, a heuristic is a practical, experience-based technique or "rule of thumb" used to solve problems, make decisions, or optimize processes when an exact, algorithmic solution is impractical, too slow, or unknown. It aims to find a good enough, though not necessarily optimal, solution efficiently, often relying on expert knowledge and historical observations.

Key Characteristics

- Experience-Based: Often derived from years of operational experience, observation, and best practices by system programmers, administrators, and developers.
- Approximation: Provides a satisfactory or "good enough" solution rather than a guaranteed optimal one, prioritizing practicality and speed in complex mainframe environments.
- Problem-Solving Aid: Used to guide decision-making in dynamic, complex, or ill-defined situations, such as performance tuning, incident response, or resource allocation.
- Adaptive: Can evolve and be refined over time as new data, system behaviors, or operational insights become available within the z/OS ecosystem.
- Efficiency-Focused: Prioritizes finding a workable solution quickly, especially in real-time operational scenarios where delays in critical mainframe systems are costly.

Use Cases

- Performance Tuning: A system programmer might use a heuristic like "if CPU utilization is consistently above 90% for a critical CICS region, check for DB2 deadlocks or inefficient SQL queries first."
- Workload Management (WLM): WLM might employ internal heuristics to dynamically adjust resource allocations (e.g., dispatching priority, CPU shares) based on observed workload behavior and system goals, even if not explicitly coded as a rigid rule.
- Problem Determination: When diagnosing an abend or system slowdown, a sysprog might apply a heuristic like "if a batch job fails with a JCL error, first check DD statements for missing datasets or incorrect DSNs."
- Capacity Planning: Estimating future CPU, DASD, or memory requirements often involves heuristics based on historical growth rates and projected business demands, rather than precise mathematical models.
- Security Monitoring: Intrusion detection systems on z/OS might use heuristic analysis to flag unusual logon patterns or resource access attempts that deviate from established norms, indicating potential threats.

Related Concepts

Heuristics are closely related to expert systems and knowledge bases in that they encapsulate practical wisdom and operational insights. They complement algorithmic solutions by providing a fallback or initial approach when algorithms are too complex or unavailable. In WLM, heuristics might inform the underlying goal-oriented resource management by providing practical guidelines for achieving service levels. They are also fundamental to problem determination methodologies and troubleshooting guides, guiding the diagnostic process for z/OS components like CICS, DB2, and IMS.

Best Practices:

Document Heuristics: Clearly document commonly used "rules of thumb" for problem diagnosis, performance tuning, and operational procedures to ensure