I need data from kafka brokers,but for fast access I am using multiple consumers with same group id known as consumer groups.But after reading by each consumer,how can we combine data from multiple consumers? Is there any logic?
By design, different consumers in the same consumer group process data independently from each other. (This behavior is what allows applications to scale well.)
But after reading by each consumer,how can we combine data from multiple consumers? Is there any logic?
The short but slightly simplified answer when you use Kafka's "Consumer API" (also called: "consumer client" library), which I think is what you are using based on the wording of your question: If you need to combine data from multiple consumers, the easiest option is to make this (new) input data available in another Kafka topic, where you do the combining in a subsequent processing step. A trivial example would be: the other, second Kafka topic would be set up to have just 1 partition, so any subsequent processing step would see all the data that needs to be combined.
If this sounds a bit too complicated, I'd suggest to use Kafka's Streams API, which makes it much easier to define such processing flows (e.g. joins or aggregations, like in your question). In other words, Kafka Streams gives you a lot of the desired built-in "logic" that you are looking for: https://kafka.apache.org/documentation/streams/