REPRO copies fewer records than expected

VSAM I/O problems — wrong records, unexpected order, failed updates — trace to keys, positioning, or status handling.

What it means

• Every VSAM verb returns a file status; ignoring it hides the real problem.
• START positions; READ NEXT follows the position.

Common causes

• Missing START before keyed reads.
• Key built from wrong positions.
• File status ignored after I/O.
• REWRITE/DELETE without a prior successful READ.

How to diagnose

• Add FILE STATUS display after each verb.
• Show the key value used.
• Verify positioning with START.

How to fix it

• Position with START before keyed access.
• Build keys from the documented layout.
• Check status after every verb.

Example: Position before keyed reads

START establishes position; READ NEXT then walks forward.

Interview tip

• Q: How would you troubleshoot a REPRO copies fewer records than expected in production?
• A: I would add file-status tracing, verify key construction and START positioning, and fix the access logic.

Prevention checklist

• Status checks on every verb.
• Centralize key-building logic.