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From "Matthias J. Sax" <matth...@confluent.io>
Subject Re: Handling of uncommitted messages
Date Fri, 01 Jul 2016 20:40:10 GMT
http://www.confluent.io/blog/hands-free-kafka-replication-a-lesson-in-operational-simplicity/

From my understanding, the watermark will not advance until both failed
follow-broker recovered and caught up.

-Matthias


On 07/01/2016 12:17 PM, Vikas Kumar wrote:
> Hi,
> 
> I have a question about handling of uncommitted messages in Kafka.
> 
> Lets say the partition has 4 replicas (1 leader, 3 followers) and all are
> currently in sync. min.insync.replicas is set to 3 and
> request.required.acks is set to all or -1.
> 
> The producer send a message to the leader, the leader appends it to it's
> log. After that, two of the replicas crashed before they could fetch this
> message. One remaining replica successfully fetched the message and
> appended to it's own log.
> 
> The leader, after certain timeout, will send an error (NotEnoughReplicas, I
> think) to the producer since min.insync.replicas condition is not met.
> 
> My question is: what will happen to the message which was appended to
> leader and one of the replica's log?
> 
> Will it be delivered to the consumers when crashed replicas come back
> online and broker starts accepting and committing new messages (i.e. high
> watermark is forwarded in the log)?
> 


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