[jira] [Created] (KAFKA-966) Allow high level consumer to 'nak' a message and force Kafka to close the KafkaStream without losing that message

["Chris Curtin (JIRA)" <ji...@apache.org>]

Chris Curtin created KAFKA-966:
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             Summary: Allow high level consumer to 'nak' a message and force Kafka to close the KafkaStream without losing that message
                 Key: KAFKA-966
                 URL: https://issues.apache.org/jira/browse/KAFKA-966
             Project: Kafka
          Issue Type: Improvement
          Components: consumer
    Affects Versions: 0.8
            Reporter: Chris Curtin
            Assignee: Neha Narkhede
            Priority: Minor


Enhancement request.

The high level consumer is very close to handling a lot of situations a 'typical' client would need. Except for when the message received from Kafka is valid, but the business logic that wants to consume it has a problem.

For example if I want to write the value to a MongoDB or Cassandra database and the database is not available. I won't know until I go to do the write that the database isn't available, but by then it is too late to NOT read the message from Kafka. Thus if I call shutdown() to stop reading, that message is lost since the offset Kafka writes to ZooKeeper is the next offset.

Ideally I'd like to be able to tell Kafka: close the KafkaStream but set the next offset to read for this partition to this message when I start up again. And if there are any messages in the BlockingQueue for other partitions, find the lowest # and use it for that partitions offset since I haven't consumed them yet.

Thus I can cleanly shutdown my processing, resolve whatever the issue is and restart the process.

Another idea might be to allow a 'peek' into the next message and if I succeed in writing to the database call 'next' to remove it from the queue. 

I understand this won't deal with a 'kill -9' or hard failure of the JVM leading to the latest offsets not being written to ZooKeeper but it addresses a likely common scenario for consumers. Nor will it add true transactional support since the ZK update could fail.


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