Failure

Enhanced Definition

In the mainframe and z/OS context, a **failure** refers to the unsuccessful completion of a program, job, transaction, or system component operation. This can manifest as an abnormal termination (`ABEND`), a non-zero return code, or an inability to perform its intended function, often requiring intervention or recovery.

Key Characteristics

- Abnormal Termination (ABEND): A common form of failure where a program or task terminates unexpectedly due to a system error (e.g., S0C4 for protection exception) or a user-requested termination (e.g., Uxxxx abend).
- Non-Zero Return/Condition Codes: Jobs or programs often indicate success with a return code of zero. A non-zero code (e.g., RC=04, RC=08) typically signifies a warning, error, or partial failure, even if the program technically completed.
- System vs. Application Failure: Failures can originate from the underlying z/OS operating system or hardware (e.g., I/O error, storage violation) or from errors within the application logic itself (e.g., division by zero, invalid data access).
- Impact on Data Integrity: Critical failures, especially in database or file updates, can compromise data integrity, necessitating rollback mechanisms or recovery procedures to restore a consistent state.
- Detection and Notification: Failures are typically detected through system messages, job logs, console alerts, or monitoring tools, often triggering automated or manual notification processes.

Use Cases

- JCL Job Failure: A batch job ABENDs with a S0C7 (data exception) because a COBOL program attempted to perform arithmetic on non-numeric data, preventing subsequent job steps from executing.
- CICS Transaction Failure: A CICS transaction fails with an APCT (abend program control table) abend due to a program attempting to access an uninitialized pointer, causing the transaction to be rolled back.
- DB2 SQL Error: A COBOL-DB2 program receives a negative SQLCODE (e.g., -911 for deadlock or -805 for package not found) when executing an SQL statement, indicating a database operation failure.
- IMS Transaction Failure: An IMS message processing program (MPP) terminates abnormally (U3001 abend) due to an application logic error, leading to the input message being requeued or discarded.
- System Component Failure: A critical z/OS component, such as a JES2 address space or a VTAM major node, fails, impacting job submission, network communication, or overall system availability.

Related Concepts

Failures are intrinsically linked to ABENDs (Abnormal Ends), which are the most common manifestation of severe program or job failures in z/OS. They necessitate robust Error Handling within application programs (e.g., ON SIZE ERROR in COBOL, SQLCODE checks in DB2) and Recovery and Restart procedures at both the application and system levels. Understanding failure types is crucial for implementing High Availability and Disaster Recovery strategies,