Ignoring COBOL File Status Checks Led to Silent Data Loss

 At first glance, it looked like a straightforward COBOL batch program.

It read a sequential file from beginning to end. For each record, it performed a random lookup in a KSDS file. If a matching record existed, it updated the record. If no match was found, it inserted a new record into the KSDS file.

Hidden deep within the program was a critical flaw: after every write operation, the program never checked the file status code to verify whether the write had succeeded.

Everything worked perfectly—until the KSDS file reached its maximum size limit of 4 GB.

Once that limit was reached, every attempt to add a new record failed. The system dutifully generated the message:

IEC070I 034(004)-220

However, because the program never validated the write status, it continued processing records as if every insert had been successful.  

The result?

New records were silently discarded while the batch job completed normally, giving everyone the illusion that everything was working as intended.

The issue remained undetected for months, quietly preventing new data from being added to the KSDS file until someone finally traced the missing records back to the unnoticed write failures.

Key Takeaway : Never assume a file operation succeeds.

After every file read, write, rewrite, delete, or open operation:

✅ Check the file status code.
✅ Handle error conditions appropriately.
✅ Log and escalate failures when necessary.