如何在Golang Kafka 10中将使用者设置为从特定偏移量开始

Question

My need is to make the producer to start from the last message it processed before it crashed. Fortunately I am in the case of having only one topic, with one partition and one consumer.

To do so I tried https://github.com/Shopify/sarama but it doesn't seems to be available yet. I am now using https://godoc.org/github.com/bsm/sarama-cluster, which allow me to commit every message offset.

I cannot retrieve the last committed offset I cannot figure out how to make a sarama consumer to start from said offset. The only parameter I've found so far is Config.Producer.Offsets.Initial.

1. How to retrieve the last committed offset?
2. How to make the consumer start from the last message whose offset has been committed? OffsetNewest will make it start from the last message produced, not the last processed b the consumer.
3. Is it possible to do so using only Shopify/sarama and not bsm/sarama-cluster ?

Thank in advance

P.S. I am using Kafka 10.0, so the offsets are stores in a kafka and not in zookeeper.

EDIT1: Partial solution: fetch all the messages since sarama.OffsetOldest and skip all of them until we found a non processed one.

Answer 1

If offset was already saved for a partition, sarama-cluster will resume consumption from that offset. The Config.Producer.Offsets.Initial option is used only if no saved offset is present (first run for a consumer group).

You can verify this by adding the following line at the beginning of your main() function:

sarama.Logger = log.New(os.Stdout, "sarama: ", log.LstdFlags)

Then you'll see something like the following in the output:

cluster/consumer CID-17db1be4-a162-411c-a106-4d198191176a consume sample/0 from 12

The 12 in that is the offset Sarama is going to start from for that partition (sample/0).