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From "Thakrar, Jayesh" <jthak...@conversantmedia.com>
Subject Re: Facing Duplication Issue in kakfa
Date Tue, 29 May 2018 13:34:32 GMT
For more details, see https://www.slideshare.net/JayeshThakrar/kafka-68540012

While this is based on Kafka 0.9, the fundamental concepts and reasons are still valid.

On 5/28/18, 12:20 PM, "Hans Jespersen" <hans@confluent.io> wrote:

    Are you seeing 1) duplicate messages stored in a Kafka topic partition or 2) duplicate
consumption and processing of a single message stored in a Kafka topic?
    If it’s #1 then you can turn on the idempotent producer feature to get Exactly Once
Semantics (EOS) while publishing.
    If it’s #2 then you can examine more closely how your consumer is doing offset commits.
    If you are committing offsets automatically by time then there is always a possibility
that the last time window of messages your consumer did not yet commit will be received again
when the consumer restarts. 
    You can instead manually commit, possibly even after each message which will shrink the
window of possible duplicate messages to 1, but at the cost of some performance. 
    What many of the Kafka Sink Connectors do for exactly once processing is to store their
offsets atomically with the data they write external to Kafka. For example a database connector
would write the message data and the offsets to a database in one atomic write operation.
Upon restart of the app it then rereads the offset from the database and resumes consumption
from Kafka from the last offset point using seek() to reposition the Kafka offset for the
consumer before the first call to poll()
    These are the techniques most people use to get end to end exactly once processing with
no duplicates even in the event of a failure.
    > On May 28, 2018, at 12:17 AM, Karthick Kumar <kkumar@apptivo.co.in> wrote:
    > Hi,
    > Facing Duplication inconsistently while bouncing Kafka producer and
    > consumer in tomcat node. any help will be appreciated to find out the root
    > cause.
    > -- 
    > With Regards,
    > Karthick.K

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