Under Min ISR Partitions Block Producer Writes

critical

availabilityUpdated Mar 2, 2026

When ISR count drops below min.insync.replicas, producers configured with acks=all will fail with NotEnoughReplicasException, blocking writes to maintain durability guarantees.

Technologies:

Apache Kafkasubject

How to detect:

Monitor kafka.replication.under_min_isr_partitions_count > 0. This indicates partitions where producers with acks=all cannot write. Cross-reference with kafka.request.produce_failed_rate to confirm producer failures.

Recommended action:

1. Check ISR status: Identify which partitions are under min ISR. 2. Restore replicas: Bring offline replicas back into ISR. 3. Review min.insync.replicas: May be set too high for current replication factor. 4. Temporary workaround: Reduce min.insync.replicas (trades durability for availability). 5. Check broker health: Address underlying broker issues causing ISR reduction. 6. Monitor producer retries: Ensure producers have appropriate retry configuration.