specify partition for one consumer in a group can not rebalance the others

I have a topic with 150 partitions [0 - 149] And I have three consumers joinning the same group.

By default, each consumer is assigned with their own ranges.

• Consumer A : [0-49]
• Consumer B : [50-99]
• Consumer C : [100-149]

I want consumer B only consumes a specific partition. Hence within its SetPartitionsRevokedHandler, only a specific one is returned.

IEnumerable<TopicPartitionOffset> OnPartitionsAssigned(IConsumer<MessageKey, byte[]> consumer, List<TopicPartition> partitions)
 {
            return new TopicPartitionOffset[]
            {
                new TopicPartitionOffset(  new TopicPartition(_topic, 0), Offset.Unset),
            };
}

I expect consumer A and C would be assigned with partition [1 - 149] I tested but it does not work in that way. Consumer A & C are not rebalanced and they are still assigned with 50 partitions each.

• Consumer A : [0-49]
• Consumer C : [100-149]

Is this a bug of client?

Confluent.Kafka nuget version : 1.2.1

• Apache Kafka version : 0.10
• Client configuration : EnableAutoCommit : false; AutoOffsetReset : Earliest

[ChadJessup]

+1 for custom partition assignors feature, I need that for kafka stream .net implementation. Image you have a joiner processor between KStream(topic1) and one KTable(topic2). Your stream application is scalable, so you must have the same subscription partition in one instance of your application. Without custom partition assignors, it’s very complicated to that, or maybe assign partition manually but more complicated.

@LGouellec - I’ve had a PR open for a few months at https://github.com/confluentinc/confluent-kafka-dotnet/pull/1133 with this.

If you’re blocked, that might help you out until some official API comes into the picture.

[ChadJessup]

+1 for custom partition assignors feature, I need that for kafka stream .net implementation. Image you have a joiner processor between KStream(topic1) and one KTable(topic2). Your stream application is scalable, so you must have the same subscription partition in one instance of your application. Without custom partition assignors, it’s very complicated to that, or maybe assign partition manually but more complicated.

@LGouellec - I’ve had a PR open for a few months at #1133 with this. If you’re blocked, that might help you out until some official API comes into the picture.

@ChadJessup I can’t see where I can set my custom partition assignor in your PR. I see your SetPartitioner(…) in ProducerBuilder, but my need is setting : Custom Partition Assignor (like JAVA Api) because with .net library, you just have both choice for partition assignor strategy (range ou roundrobin)

@LGouellec - you’re right, sorry - I got confused on partitioners and assignors. I’m taking a look at adding assignors here real soon as a PR, but it’ll probably wait on feedback on whatever happens with #1297