Glossary

Effective consumers (Kafka lag)

Effective consumers is the actual number of consumer instances actively processing partitions, capped at the partition count: effective = min(running_consumers, partition_count). Consumers beyond the partition count sit idle and contribute no throughput. Adding instances does not reduce lag once you have reached consumer saturation.

Formula: effective_consumers = min(running_consumers, partition_count); only way past saturation is more partitions.

Last updated: March 2026