Proper way to reset offset for a given GroupId

Description

I need to be able to “rewind” a consumer to the beginning of a topic and re-process existing messages. Is this properly supported?

I’m using the following code, but am not getting the expected result.

foreach (var topicPartition in Consumer.Assignment)
{
	Consumer.Assign(new TopicPartitionOffset(topicPartition, Offset.Beginning));
}

I’ve tried both .Seek() and .Assign() in the code above.

What is the proper way of resetting the offset on a per-group basis?

Checklist

• [1.0.1.1 ] Confluent.Kafka nuget version.

[russau]

FWIW This appears to be working for me with ver 1.3.0:

var consumer = new ConsumerBuilder<string, string>(consumerConfig)
.SetPartitionsAssignedHandler((c, partitions) =>
{
    var offsets = partitions.Select(tp => new TopicPartitionOffset(tp, Offset.Beginning));
    return offsets;
})
.Build();
....

[harvzor]

if you don’t want to need to stop your consumers, you’ll need to signal them in some way that they should start reprocessing, then you could use IConsumer.QueryWatermarkOffsets to get the beginning offset for each partition, then seek to that position, then commit as usual after consuming messages.

This appears to be the suggested code:

private void ResetOffset()
{
    // Assume partition 0, good luck finding out what your partition is otherwise!
    var topicPartition = new TopicPartition(_topic, new Partition(0));
    var watermarkOffsets = _consumer.QueryWatermarkOffsets(topicPartition, TimeSpan.FromSeconds(1));
    _consumer.Seek(new TopicPartitionOffset(topicPartition, watermarkOffsets.Low));
}

Which would work about 50% of the time, with the other half throwing an “erroneous” exception.