WRITE with uniqueness check vs REWRITE for idempotent record handling

Ensuring Idempotency in Indexed File Writes

When implementing retry logic for data persistence in COBOL, preventing duplicate records is critical. In environments using indexed files, developers must decide between two primary patterns to handle potential retries without duplicating writes.

One approach utilizes the WRITE statement combined with a manual check of a unique transaction ID or the capture of File Status 22 to detect duplicates. The alternative approach uses the REWRITE statement to update an existing record by its key, effectively ensuring that a retry simply overwrites the previous attempt.

The decision involves a trade-off between the overhead of initial record creation and the safety of subsequent updates. There is uncertainty regarding how different vendor implementations handle file pointer consistency during a failed WRITE retry before a successful REWRITE is issued.

• Does the REWRITE approach introduce significant performance degradation compared to a WRITE with a status check?
• How is file pointer stability maintained across vendor-specific COBOL runtimes during a retry sequence?