CICS Debugging

CICS debugging involves identifying and resolving issues in online transaction processing applications. CICS provides several diagnostic facilities including CEDF (Command-level Execution Diagnostic Facility), abend dumps, trace entries, and performance monitoring tools. Understanding these debugging techniques is essential for maintaining reliable CICS applications and quickly resolving production issues. Effective debugging requires knowledge of CICS internals, program execution flow, and the ability to interpret diagnostic output.

Understanding CICS Debugging

Debugging in CICS differs significantly from traditional program debugging because transactions execute in an online environment with multiple concurrent users. CICS debugging facilities allow you to trace command execution, examine data areas, capture error conditions, and analyze system behavior without disrupting other users. The main debugging tools are CEDF for interactive debugging, abend dumps for post-mortem analysis, and trace facilities for performance and execution analysis.

Think of CICS debugging like being a detective investigating a crime scene. CEDF is like having surveillance cameras that let you watch what happens step by step. Abend dumps are like photographs taken at the moment something went wrong, capturing the exact state. Trace entries are like security logs that record who did what and when. By combining these tools, you can reconstruct what happened and figure out why a problem occurred.

CEDF - Command-level Execution Diagnostic Facility

CEDF is an interactive debugging tool that allows you to step through CICS commands, examine and modify storage, and control program execution. It provides a step-by-step view of CICS command processing, showing exactly what happens when each EXEC CICS command executes.

To start CEDF, enter "CEDF" in the CICS transaction ID field. CEDF will then prompt for the transaction to debug. Once started, CEDF displays each CICS command before and after execution, allowing you to examine command parameters, response codes, and affected data areas.

Using CEDF Commands

While debugging with CEDF, you can use various commands to control execution and examine data:

• D EIB: Display all EIB (Execute Interface Block) fields
• D [data-name]: Display the contents of a data area
• M [data-name] = value: Modify the contents of a data area
• T [transaction-id]: Switch debugging to another transaction
• GO: Continue execution to next breakpoint
• STEP: Execute next command only

These commands allow you to dynamically examine and modify program state during debugging, making it easier to isolate problems and test fixes.

Abend Dumps

When a CICS transaction abends abnormally, the system generates an abend dump containing a snapshot of the transaction state at the time of failure. The dump includes program storage dumps, register contents, control blocks, and execution history. This information is critical for post-mortem analysis when a transaction fails unexpectedly.

Abend dumps are automatically generated when a transaction abends (unless suppressed by HANDLE ABEND with CANCEL). The dump is written to the dump data set or displayed at the terminal, depending on system configuration. Analyzing dumps requires understanding assembly language, program structure, and CICS control blocks.

Analyzing CICS Dumps

The key areas to examine in a CICS dump include:

• Program Status Word (PSW): Shows the failing instruction and condition code
• General Purpose Registers: Contain addresses and values at failure time
• Program Base Address: Starting address of the failing program
• Storage Areas: The contents of memory at various addresses
• Control Blocks: EIB, TCA, and other CICS control structures

Use IPCS (Interactive Problem Control System) or formatted dump listing to analyze these components. Trace backward from the failing instruction to understand the sequence of events leading to the abend.

CICS Trace Facilities

CICS provides comprehensive tracing capabilities to capture execution details for performance analysis and problem diagnosis. The General Trace Facility (GTF) and CICS trace entries record command execution, resource usage, and system events.

Enable tracing using CEMT commands or through system initialization parameters. Configure trace classes to capture specific events such as command execution, file operations, or temporary storage access. Trace data can be captured to temporary queues or data sets for later analysis.

Performance Debugging

Performance issues in CICS require specialized debugging techniques. Monitor response times, identify bottlenecks, and analyze system resource usage. Use CICS Performance Analyzer (CPA) to collect and analyze performance data.

Common performance problems include excessive file I/O, inefficient search algorithms, resource contention, and database deadlocks. Use trace data to identify the specific operations consuming time and optimize those areas.

Debugging Best Practices

Follow these practices for effective CICS debugging:

• Use CEDF for interactive debugging: Step through commands to understand execution flow
• Capture abend dumps: Always capture dumps for abend analysis
• Enable trace strategically: Use trace for specific problem areas to avoid performance impact
• Document your findings: Keep records of debugging sessions and resolutions
• Test fixes carefully: Verify fixes in test environment before production
• Understand the full context: Don't just look at the failing instruction, understand the entire execution path
• Use appropriate tools: Match debugging tools to the problem type (CEDF for logic errors, dumps for abends, trace for performance)

Explain Like I'm 5: CICS Debugging

Imagine a toy that stopped working:

• CEDF is like taking the toy apart piece by piece while it's running to see exactly where it gets stuck
• Abend dump is like taking a photo of the broken toy exactly as it failed, so you can look at it later
• Trace is like a diary that writes down everything the toy does and when it does it

By using these tools together, you can figure out what broke and how to fix it!

Practice Exercises

Complete these exercises to reinforce your CICS debugging skills:

Exercise 1: Using CEDF

Start CEDF and step through a simple CICS transaction. Use D commands to examine EIB fields and data areas. Modify a data item using M command and observe the effect on execution.

Exercise 2: Analyzing a Dump

Review a CICS abend dump (real or practice dump). Identify the failing instruction from the PSW. Examine register contents and trace the execution path leading to the abend.

Exercise 3: Enabling Trace

Enable CICS trace for file operations using CEMT. Run a transaction that performs file I/O and examine the trace output. Identify each file command and its parameters.

Exercise 4: Performance Analysis

Use CICS Performance Analyzer to identify performance bottlenecks in a test transaction. Identify the slowest operations and suggest optimizations.

Exercise 5: Debugging Workflow

Create a debugging workflow for a simulated abend situation. Document the steps from initial problem report through resolution using CEDF, dumps, and trace data.

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