Interview lab: design, troubleshoot and code

Use a repeatable answer frame

For a design question, state the business goal and constraints first. Then name the object or service you would use, show the data and job flow, and explain authority, commitment, monitoring, and recovery. End with one trade-off and one test that would change your decision.

For a troubleshooting question, state the symptom you would measure, the first log or command you would inspect, and the safe mitigation. Interviewers are looking for a controlled investigation, not a list of commands.

1. Clarify the goal and constraints
2. Choose the smallest IBM i design that fits
3. Name failure, authority, and consistency behavior
4. Describe observability and recovery
5. Give a test and a measured trade-off

Find the hidden failure window

Tricky questions often hide an assumption: a library list is stable, a queue entry is processed once, a record is unlocked, a service program interface never changes, or a batch job can simply be rerun. Challenge the assumption and offer a safer design with an operator path.

When a requirement is ambiguous, state what you would ask before coding. A short clarifying question can prevent a technically correct answer from solving the wrong problem.

A compact investigation checklist

DSPJOB JOB(*) OPTION(*JOBLOG)
DSPLIBL
DSPOBJAUT OBJ(APPDATA/*ALL) OBJTYPE(*ALL)
WRKACTJOB SBS(*ALL)
DSPJOBQ JOBQ(APPDATA/BATCHQ)

Explain code in both RPG styles

The fixed and fully free examples should express the same business behavior. In an interview, describe the input, lookup, status check, update, and test cases before showing source. Mention what you would add in production: prototypes, error handling, commitment scope, logging, and a concurrency decision.

Keep the code skeleton intentionally small. The goal is to show safe control flow and the questions you would resolve with the team, not to pretend a five-line snippet is a complete application.

Safe update skeleton

FProducts        UF   E             K DISK
C     productId    CHAIN     ProductRec
C                   IF        %FOUND(Products) AND newQty >= 0
C                   EVAL      quantity = newQty
C                   UPDATE    ProductRec
C                   ENDIF

**FREE
dcl-f Products keyed usage(*update);
chain productId ProductRec;
if %found(Products) and newQty >= 0;
  quantity = newQty;
  update ProductRec;
endif;