Overview
A consumer group is a set of consumers that jointly consume a topic: each partition is consumed by exactly one consumer in the group at any given time. If there are fewer consumers than partitions, some consumers handle several partitions. Extra consumers receive no partitions until another member leaves or partitions are added. Each consumer group receives every message independently, and the KafkaConsumer Javadoc notes that groups work without duplicating data. (Share groups, KIP-932, are a different group type with different rules.)
Analogy
Production tip
Check yourself
A topic has 3 partitions and a consumer group has 5 consumers. What happens?
Sources
- KafkaConsumer Javadoc (4.2) (opens in a new tab)
- Basic Kafka operations (4.2 documentation) (opens in a new tab)
- Design (4.2 documentation) (opens in a new tab)
Checked against Kafka 4.2 documentation on Oct 2026. Draft: not yet reviewed by a Kafka specialist. Releases move on, so confirm against the current documentation before you act on a number.