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From Dennis Haller <dhal...@talemetry.com>
Subject Re: How does Kafka decide which Consumer out of multiple Consumer clients to assign to a single topic partition
Date Thu, 22 Aug 2013 17:44:37 GMT
The sorted list makes sense with what I'm seeing.

The consumers are named with the group-name appended with the server
hostname plus some other string such as this:
redis-indexer_ip-10-122-123-214.ec2.internal-1377184713770-a6aa2f8e-0

Because in AWS the hostname is coming up with a different internal ip
address  each time, then the consumer instances will sort in different
order with respect to the machine names from one deployment to another.

Dennis



On Thu, Aug 22, 2013 at 9:31 AM, Guozhang Wang <wangguoz@gmail.com> wrote:

> Hello Dennis,
>
> The rebalance on each consumer works by first release their owned
> partitions first (releasePartitionOwnership in
> ZookeeperConsumerConnector.scala) and then compute the new ownership. Hence
> in your scenario it is equally possible for each one of the two consumers
> to own the partition in each rebalance process. And it is  not possible to
> predict which consumer will claim the ownership of the partition.
>
> Guozhang
>
>
> On Thu, Aug 22, 2013 at 8:53 AM, Dennis Haller <dhaller@talemetry.com
> >wrote:
>
> > I have a situation where two high level consumers are being created to
> > consume a single topic. There is only one partition for the topic, so I
> > understand that only one Consumer will end up owning the topic and
> > receiving messages. The two consumers are created from two servers in a
> > redundant master - slave configuration, and it is our intention that the
> > servers should start in the same configuration predictably, with all the
> > Consumers active on the master server.
> >
> > However, we find after both Consumers have been created that sometimes
> the
> > first Consumer client succeeds in owning the topic and sometimes it is
> the
> > second. I first thought that the first Consumer  client to register with
> > the topic would be retained even if subsequent Consumers also register
> for
> > the topic, but I see sometimes the second Consumer client succeeds in
> > replacing the first Consumer.
> >
> > The logs show a rebalancing algorithm working after each Consumer is
> > registered.
> >
> > In this case, where there is only one topic-partition, is it possible to
> > predict what Consumer client will own the topic? How is that rebalancing
> > done?
> >
> > Thanks
> > Dennis
> >
>
>
>
> --
> -- Guozhang
>

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