Kafka guarantees that messages within a partition are ordered by their offset, which is a unique identifier assigned to each message as it is produced. This ensures that messages are processed in the order in which they were produced, even if they are produced by different producers or at different times.
Kafka uses a leader-follower replication mechanism to replicate data across multiple brokers in a Kafka cluster. Each partition has one leader broker that receives all write requests for that partition, while the other brokers act as followers that replicate the data from the leader. The leader broker is responsible for assigning unique offsets to each message as it is produced.
When a consumer reads messages from a partition, it maintains an offset to keep track of the last message it has consumed. Kafka allows consumers to specify the offset they want to start reading from, so they can start reading from the beginning of the partition or from a specific offset.
Kafka also uses a mechanism called “consumer groups” to ensure that each message is consumed by only one consumer in a group. Consumer groups allow multiple consumers to read from the same partition in parallel, but each message is consumed by only one consumer within the group.
Overall, Kafka’s use of unique offsets and leader-follower replication ensures that messages within a partition are ordered and processed in the correct order, even in the presence of multiple producers and consumers.