Attempt to insert unique descriptor shows on plog?

On reading the plog we have a BI (before image) for a record, and an after image for a record with the same ISN. It has the same CID and time.

From APAS reports, we can see that there was an attempt to create this record, at exactly that time, but that it failed with an Adabas response 198. (The descriptor is Unique, so the response 198 is valid).

I thought the plog only showed transactions that Adabas accepted and completed successfully, so am surprised to see a failed transaction and its reversal show up in there.

Is this what we expect Adabas to do?


Correct. The PLOG includes failed transactions, but they won’t have an ET.

The PLOG (Protection Log) tracks incomplete modifications as they happen, allowing Adabas to roll them back to a known, consistent state during recovery. Updates may or may not be applied to the disk as they happen (depending on buffering), so the PLOG rollback needs to know what transactions are inflight, not just the completed ones.