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CPDUMP - Coupling Facility Dump

Enhanced Definition

A CPDUMP (Coupling Facility Dump) is a specialized diagnostic tool in IBM z/OS used to capture the contents of a specific Coupling Facility (CF) structure or the entire CF for problem determination. It provides a snapshot of the CF's memory, control blocks, and data at a given point in time, crucial for diagnosing issues related to sysplex-wide data sharing and resource management.

Key Characteristics

- Scope: Can capture either a specific CF structure (e.g., a lock structure, cache structure for DB2 or IMS) or the entire Coupling Facility's memory contents.
- Initiation: Typically initiated via the MVS DUMP command with the CF keyword (e.g., DUMP CF,STRNAME=structure_name or DUMP CF,CFNAME=cf_name).
- Output: The captured data is written to a pre-allocated DUMP dataset (often a SYS1.DUMPxx dataset) on a DASD volume, similar to other z/OS system dumps.
- Purpose: Primarily used by IBM support and system programmers to analyze complex problems involving CF structures, data integrity, inter-system communication, and sysplex failures.
- Impact: Taking a CPDUMP can be resource-intensive and may temporarily impact CF performance or availability, especially for full CF dumps, due to the data transfer involved.
- Analysis: The contents of a CPDUMP are analyzed using the Interactive Problem Control System (IPCS), which provides commands to format and interpret the raw dump data.

Use Cases

- Diagnosing CF Structure Corruption: When applications or systems report errors related to data integrity within a shared CF structure (e.g., DB2 Group Buffer Pool, IMS Shared Queues, CICS Shared Data Tables).
- Troubleshooting Sysplex Communication Issues: Investigating problems where systems in a sysplex are unable to communicate or synchronize properly through the CF, leading to hangs or deadlocks.
- Analyzing CF Performance Bottlenecks: Examining the state of CF structures and their usage patterns to identify potential performance bottlenecks, contention, or excessive CF path usage.
- Debugging Application-CF Interactions: Providing detailed insights into how an application (e.g., CICS, DB2, IMS) is interacting with its assigned CF structures when unexpected behavior or abends occur.

Related Concepts

A CPDUMP is intrinsically linked to the Coupling Facility (CF), which is a specialized hardware component providing high-speed caching, list processing, and locking services for a z/OS sysplex. It complements other z/OS diagnostic tools like SVC Dumps and Stand-Alone Dumps, but specifically targets the CF's internal state. The analysis of a CPDUMP heavily relies on IPCS (Interactive Problem Control System), which is the standard z/OS utility for formatting and interpreting all types of system dumps. It helps diagnose issues impacting critical sysplex components like Global Resource Serialization (GRS), DB2 Data Sharing, CICSplex, and IMS Shared Queues, all of which heavily utilize CF structures for inter-system coordination and data integrity.

Best Practices:

Targeted Dumps: Whenever possible, take a dump of a specific structure (STRNAME) rather than the entire CF (CFNAME) to minimize impact and simplify analysis, unless a full CF dump is explicitly requested by support.
Timeliness: Capture the CPDUMP as close as possible to the occurrence of the problem to ensure the most relevant diagnostic information is present, ideally *before* any recovery actions clear the problematic state.