Medium severitysql
Power BI Refresh Error:
CONCURRENT_APPEND
What does this error mean?
A streaming or batch append transaction failed because a concurrent transaction appended data to the same partition or table section, invalidating the first transaction's read snapshot. This is specific to append operations with non-overlapping data.
Common causes
- 1Multiple streaming jobs are writing to the same Delta table without unique checkpoint locations
- 2Two batch jobs run in parallel and both append to the same partition at the same time
- 3A streaming checkpoint was copied and two stream instances started with the same checkpoint, causing duplicate commits
- 4A pipeline restart created a second instance before the first was fully shut down
How to fix it
- 1Ensure each streaming query has a unique checkpoint location — never share checkpoints between two stream instances.
- 2For batch jobs, add explicit job dependencies so only one appends at a time, or partition the output so each job writes to a unique partition.
- 3After a restart, confirm the previous streaming query has stopped before starting the new one.
- 4Retry the failed append — if it was a true race condition with no duplicate checkpoint, the retry will succeed.