Diagnostics

Enhanced Definition

In the z/OS environment, diagnostics refers to the systematic process and specialized tools used to identify, analyze, and resolve problems within the operating system, its subsystems, applications, or underlying hardware. It involves collecting and interpreting various forms of data to pinpoint the root cause of an issue and facilitate its resolution. In the mainframe context, diagnostics refers to the systematic process and the resulting information used to identify, analyze, and resolve problems or abnormal conditions within z/OS, applications, or hardware components. It involves collecting and interpreting various data sources to understand the root cause of an issue, ranging from application errors to system crashes.

Key Characteristics

- System Dumps: Generation of various types of dumps (e.g., SVC dumps, stand-alone dumps, transaction dumps like CICS system or transaction dumps) that capture the state of memory, registers, and control blocks at a specific point in time for post-mortem analysis.
- Log Files and Journals: Analysis of critical system logs (SYSLOG, SMF records, RMF reports), job logs (SYSOUT), and application-specific logs (e.g., CICS MSGUSR, DB2 DSNMSTR address space messages, IMS LOGREC) to trace events and error messages.
- Traces: Utilization of system-level traces (GTF, SLIP), component traces (e.g., CICS CTRA, DB2 DB2PM traces), or application-level traces to record sequences of events, program flow, and resource usage.
- Monitoring Tools: Employment of performance and availability monitoring tools (e.g., RMF, OMEGAMON, SYSVIEW) to observe system resource utilization, identify bottlenecks, and detect anomalies in real-time or through historical data.
- Error Codes and Messages: Interpretation of system completion codes (ABEND codes like S0C4, S0C7), return codes from programs, and console messages (WTO) to understand the nature and location of an error.
- Problem Management Records (PMRs): The formal process of packaging diagnostic data (dumps, logs, traces) and submitting it to vendors (e.g., IBM Support) for expert analysis and resolution of complex or undocumented issues.

Use Cases

- Application ABEND Resolution: Analyzing SVC dumps, job logs, and SYSOUT for a COBOL or PL/I program that terminated abnormally to determine the exact instruction causing the ABEND (e.g., S0C4 for protection exception, S0C7 for data exception).
- Performance Bottleneck Identification: Using RMF reports and SMF data to identify high CPU consumption, I/O contention, or memory constraints impacting the overall performance of z/OS, a specific LPAR, or critical applications.
- CICS Transaction Failure Analysis: Examining CICS transaction dumps, MSGUSR logs, and CICS trace entries to diagnose issues such as storage violations, deadlocks, or program logic errors within a CICS region.
- DB2 Query Optimization and Issues: Reviewing DB2 Explain output, SMF type 101 records, and DB2 trace data to understand query access paths, identify inefficient SQL, or diagnose database contention problems.
- Operating System Malfunctions: Collecting stand-alone dumps or SVC dumps for critical z/OS system failures (e.g., wait states, system loops, IPL issues) to assist IBM Support in diagnosing kernel-level problems.

Related Concepts

Diagnostics are fundamental to system reliability and high availability in the mainframe environment. They rely heavily on the data generated by the z/OS operating system, its subsystems (CICS, DB2, IMS), and applications written in languages like COBOL or PL/I. Effective diagnostic processes are often triggered by monitoring tools and are critical for maintaining the Service Level Agreements (SLAs) associated with enterprise computing. The interpretation of diagnostic data frequently requires an understanding of JCL, assembler, and the internal workings of various z/OS components.

Best Practices:

Proactive Monitoring and Alerting: Implement robust monitoring solutions (RMF, OMEGAMON) with predefined thresholds and automated alerts to detect potential issues (e.g., high CPU, full datasets) before they lead to outages.
Standardized Dump Procedures: Establish clear, documented procedures for generating and collecting various types of dumps (e.g., SLIP traps for specific ABENDs), ensuring that critical diagnostic data is consistently captured.
Centralized Log Management: Utilize tools for centralizing, archiving, and analyzing SYSLOG, SMF, job logs, and application logs to facilitate quicker search, correlation, and identification of problem patterns.
Knowledge Base and Runbooks: Maintain a comprehensive knowledge base of common issues, their diagnostic steps, and documented resolutions (runbooks) to empower support teams and reduce resolution times.
Regular Training and Skill Development: Ensure that technical staff