Kafka: Spring @KafkaListener concurrency maps to partitions

concurrency creates that many consumer threads in the group - capped by the partition count.

Code

@KafkaListener(topics = "orders", groupId = "orders-service", concurrency = "3")
void onOrder(ConsumerRecord<String, String> record) { ... }

Output

3 partitions -> 3 threads, one each
6 partitions -> 3 threads, two each
2 partitions -> 3 threads, one permanently idle

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Published 2026-08-11