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Kafka Consumer Lag Triage

Decide whether lag is a capacity problem, a poison message, or skew.

Triages consumer lag from the consumer-group offsets: distinguishing a slow consumer, a partitioned hot key, a rebalance storm, and a poison-pill retry loop.

npx de-agent-platform add kafka-consumer-lag-triage

At a glance

What Decide whether lag is a capacity problem, a poison message, or skew.
Where Kafka · tech-kafka

Learning objectives

  • Read per-partition lag to separate skew from throughput
  • Detect a rebalance loop from consumer-group state
  • Find the poison message from retry counts

Security scan

Last sweep 2026-10-24: 0 finding(s), 0 marked as examples.

Details

Kafka Consumer Lag Triage

Three questions

  1. Is lag rising, flat, or falling? Flat at a high number is fine; rising is not.
  2. Is lag even across partitions? Skew means a hot key, not capacity.
  3. Is the consumer group stable? Frequent PreparingRebalance is the real bug.

Signatures

  • Lag on one partition only → key skew; re-key or increase partitions.
  • All partitions rising, CPU low → downstream (DB/API) is the bottleneck.
  • Lag resets to zero then climbs → rebalance loop; check session.timeout.ms.
  • One offset stuck, others advance → poison message in a retry loop.

Never

Do not "fix" lag by resetting offsets. That is data loss wearing a hat.

Registry stats

Verification community · Sep 20, 2026
Completeness 100
Trust multiplier ×0.5
Composite 33.5 · adequate
Freshness 34 days since last source check
Difficulty advanced
Version 0.1.3
License Apache-2.0
Security flags 3