Kafka Exception CoordinatorLoadInProgressException
In the context of the group coordinator, the broker returns this error code for any coordinator request if it is still loading the group metadata (e.g. after a leader change for that group metadata topic partition). In the context of the transactional coordinator, this error will be returned if there is a pending transactional request with the same transactional id, or if the transaction cache is currently being populated from the transaction log.
Common Causes
- The __consumer_offsets partition coordinator broker just became the leader and is loading committed offsets from the log into memory
- Coordinator broker restarted or the partition was reassigned, triggering a reload of potentially millions of offset records
- Large number of consumer groups with long offset histories causing slow coordinator startup under GC pressure
Solutions
- This is transient and retriable by design; ensure consumer client's 'retry.backoff.ms' and coordinator retry logic are configured to wait (default 100ms); typically resolves in seconds
- If it lasts for minutes, inspect the broker leading the affected __consumer_offsets partition for GC pauses, slow disk, or log recovery delay; the coordinator cannot serve the group until offset load finishes
- Reduce long-term coordinator load by expiring unused groups with offsets.retention.minutes, cleaning up dead groups, and keeping __consumer_offsets healthy and compacted
Example Stack Trace
org.apache.kafka.common.errors.CoordinatorLoadInProgressException: The coordinator is loading and hence can't process requests.Diagnostic Commands
# Look for coordinator loading events in logs
grep -E 'Loading offsets|Finished loading offsets|CoordinatorLoadInProgress' /var/log/kafka/server.log | tail -20
# List all consumer groups
kafka-consumer-groups.sh --bootstrap-server localhost:9092 --list 2>&1 | head -5Related
Protocol error: COORDINATOR_LOAD_IN_PROGRESS (code 14)
Related Consumer exceptions: CommitFailedException · CoordinatorNotAvailableException · FencedInstanceIdException · FencedMemberEpochException · GroupMaxSizeReachedException · IllegalGenerationException · InvalidGroupIdException · InvalidOffsetException
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