Kafka Consumer not consuming from last commited offset after restart

Question

I have a consumer polling from subscribed topic. It consumes each message and does some processing (within seconds), pushes to different topic and commits offset.

There are totally 5000 messages,

before restart - consumed 2900 messages and committed offset

after restart - started consuming from offset 0.

Even though consumer is created with same consumer group, it started processing messages from offset 0.

kafka version (strimzi) > 2.0.0 kafka-python == 2.0.1

Answer 1

We don't know how many partitions you have in your topic but when consumers are created within a same consumer group, they will consume records from different partitions ( We can't have two consumers in a consumer group that consume from the same partition and If you add a consumer the group coordinator will execute the process of Re-balancing to reassign each consumer to a specific partition).

I think the offset 0 comes from the property auto.offset.reset which can be :

• latest : Start at the latest offset in log
• earliest : Start with the earliest record.
• none : Throw an exception when there is no existing offset data.

But this property kicks in only if your consumer group doesn't have a valid offset committed.

NB: Records in a topic have a retention period log.retention.ms property so your latest messages could be deleted when your are processing the first records in the log.

Questions: While you want to consume message from one topic and process data and write them to another topic why you didn't use Kafka Streaming ?