First Failure

Enhanced Definition

In the context of mainframe systems, "first failure" refers to the initial error, anomaly, or event that triggers a chain of subsequent problems, system abends, or application failures. It represents the earliest detectable symptom or the root cause of a larger issue, making its identification crucial for effective problem determination.

Key Characteristics

- Root Cause Indicator: Often points directly to the underlying defect, resource contention, or logical error, rather than just a symptom.
- Chronological Precedence: It is the earliest event in a sequence of errors, even if other more severe symptoms manifest later.
- Diagnostic Focus: Serves as the primary target for analysis during problem determination (PD) to prevent recurrence.
- Logged Evidence: Typically recorded in system logs (SYSLOG), job logs, application logs (e.g., CICS MSGUSR), or captured in system dumps (e.g., SVC dump, CICS dump) with specific error codes or messages.
- Cascading Impact: Can lead to a series of secondary failures, performance degradation, or system instability if not addressed.

Use Cases

- Problem Determination (PD) for Abends: When a batch job or online transaction abends, identifying the first failure in the job log or system log helps pinpoint the exact line of code, resource issue, or data error that caused the termination.
- System Stability Analysis: Diagnosing an unscheduled IPL (Initial Program Load) or system hang by examining SVC dumps and SYSLOG to find the initial operating system component failure or resource exhaustion.
- Application Troubleshooting: Investigating a CICS transaction failure by analyzing the CICS dump and MSGUSR log to trace back to the first program error, file I/O issue, or database access problem.
- Performance Bottleneck Identification: Pinpointing an initial resource contention (e.g., ENQ contention, DB2 latch contention) that subsequently leads to broader system slowdowns or timeouts.

Related Concepts

The first failure is central to Problem Determination (PD), as it guides the analysis of dumps (SVC, CICS, Standalone) and system logs (SYSLOG, SMF, job logs) to uncover the root cause of an abend or system issue. It often manifests as a specific error code or message, which then directs further investigation using trace facilities (e.g., GTF, CICS trace) to understand the sequence of events leading to the failure.

Best Practices:

Implement Robust Logging: Ensure SYSLOG, SMF, and application-specific logs are adequately configured to capture detailed error messages and events.
Prioritize Dump Analysis: Train technical staff in effective SVC dump and CICS dump analysis to quickly identify the first failure and its context.
Automate Alerting: Configure monitoring tools to generate immediate alerts for critical error messages or conditions indicative of a first failure.
Maintain Error Code Documentation: Keep comprehensive and up-to-date documentation for common mainframe error codes and their associated first failure scenarios.
Utilize Trace Facilities Judiciously: Employ system and application trace facilities (GTF, CICS trace, DB2 trace) to capture granular event sequences when a first failure is difficult to isolate.