[GitHub] [pulsar] duyhieuvo commented on issue #3504: Failover mode consumer has inconsistent behaviour

[GitBox <gi...@apache.org>]

duyhieuvo commented on issue #3504:
URL: https://github.com/apache/pulsar/issues/3504#issuecomment-749442252


   Hi @merlimat. I think this behavior can be problematic. Please correct me if I don't understand it correctly. Assuming an application reads messages from Pulsar, processes and produces results back to another Pulsar topic. 
   If there are still some unacknowledged messages buffering on the disconnected consumer and these messages are re-sent to the failover consumer, these messages can be concurrently processed in two different processes. This can lead to duplication or out-of-order results on the output topic. 
   Does Pulsar provide any fence-off mechanism to prevent application with disconnected consumer from continuing to produce results to Pulsar? For example, in case of Apache Kafka, they use a new epoch number for the producer on the failover instance to detect and drop any message produced by the instance with disconnected consumer.


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