If a consumer group is subscribed to multiple topic partitions how does kafka decide which it will read first?

Question

I am trying to build a application that can read through a kafka topic but I need it to have a "see previous" button. I know how to seek through a particular partition but is it possible to back through all the messages in a topic in the order that they were read in? I am using Java KafkaConsumer.

Answer 1

Offsets are per partition and there is no ordering between messages across different partitions. You can't go back through all the messages in a topic in the order that they were read in as kafka doesn't know the order in which the consumer read in messages from different partitions (different partitions may be read from different brokers across the cluster). However, what you could do is do ordered buffering in your app as you read messages in, that would allow you to go back as far as the buffer capacity.