Glossary

Consumer lag (Kafka)

Consumer lag is the difference between the Log End Offset (latest message written to a partition) and the Consumer Committed Offset (last position the consumer group has confirmed processing) per partition. Total group lag = sum of per-partition lags. Growing lag is the primary indicator that consumers cannot keep up with produce rate.

Formula: lag_per_partition = log_end_offset − committed_offset. lag_growth_rate ≈ produce_rate − min(consumers, partitions) × per_consumer_throughput (msg/s).

Last updated: March 2026