Flink-Kafka consumers for multiple topics

Question

I have a Flink Kafka consumer which reads from multiple kafka-topics(3 in my case). There are 5 partitions per topic on kafka. How many consumers does Flink create by default.

Is it:

1. 5 consumers per topic. ie. in all 15 consumers
2. 5 consumers in all.

The consumption of kafka messages is very slow, So I am not able to figure the number of consumers attached to each topic.

Answer 1

The number of consumers is equal to the parallelism of the source function. There is only one consumer for each parallel instance of the source operator. If you've left the parallelism unconfigured, I think it might default to a parallelism of one, which would certainly explain the slowness.

If you're running a standalone cluster, the webGUI will show you the parallelism of your source function while it's running.