Partition

A partition is a subdivision of a topic.

Each partition is:

• ordered
• append-only
• independent

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Example

Topic: order.created.v1

Partition 0
Partition 1
Partition 2

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Why Partitions Exist

1. Scalability

Multiple consumers can process in parallel.

2. Performance

Data is distributed across brokers.

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Ordering Rule

Kafka guarantees ordering only within a partition.

Example

Partition 0: offset 0 → A
offset 1 → B
offset 2 → C

Order is guaranteed.

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Across partitions:

Partition 0 → A, B
Partition 1 → C, D

Order is NOT guaranteed globally.

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How Producer Decides Partition

With Key

kafkaTemplate.send("orders", "user1", event);

Same key → same partition → ordering guaranteed

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Without Key

Kafka distributes messages randomly.

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Kafka CLI — Describe Topic

kafka-topics.sh   --describe   --topic order.created.v1   --bootstrap-server localhost:9092

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