Skip to content
Kafka Is FunProgress

Intermediate5 min

Understanding HWM vs LEO

Visualize the gap between Log End Offset and High Watermark and understand consumer visibility.

The HWM/LEO distinction is one of Kafka's most subtle but important concepts. Consumers can only read up to HWM. Messages between HWM and LEO are committed by the leader but not yet confirmed by all ISR members.

The steps below reference the interactive simulator, which is being migrated into /simulate next — until it lands, treat this as the written runbook for the exercise.

Steps

0 of 5 steps completed

Verification

You can read LEO, HWM, and consumer offsets from the visualizer and explain the relationship.

The interview angle

HWM is the consumer's visibility boundary. LEO is the write frontier. The HWM/LEO gap represents 'written but not yet durably committed' data.