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javaapache-kafkakafka-consumer-apispring-kafka

What is Spring KafkaListener reading strategy with severals topics?

How Kafka works with severals topics?

 @KafkaListener(topics = {"topic1" , "topic2"}, groupId = "groupid")

For example:

  • "topic1" has "topic1_message1","topic1_message2" entities on a single partition
  • "topic2" has "topic2_message1","topic2_message2" entities on a single partition

What will be the reading order?

  • "topic1_message1","topic1_message2","topic2_message1","topic2_message2"
  • "topic1_message1","topic2_message1","topic1_message2","topic2_message2"

Or server will instanciate two threads which are reading both topics concurently?

Solution

  • both of these are true. it is randomly

    • "topic1_message1","topic1_message2","topic2_message1","topic2_message2"
    • "topic1_message1","topic2_message1","topic1_message2","topic2_message2"

    because they are on single partition one thing you should know;

    1. "topic1_message1" comes before "topic1_message2"
    2. "topic2_message1" comes before "topic2_message2"