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From Chris Horrocks <ch...@hor.rocks>
Subject Re: Kafka Sink random partition assignment
Date Tue, 07 Jun 2016 18:36:55 GMT
You can implement sink groups load balance processor (https://flume.apache.org/FlumeUserGuide.html#flume-sink-processors)
to spread the load over multiple producers to partly account for situation where you might
have one kafka sink rotating between mutliple partitions, it's not an exact science though
as you'd need multiple kafka sinks (n number more than you have partitions in the topic being
written to) in order to make the balance of probabilities such that you were always writing
to each partition from at least one sink.

As with all hadoop technologies: depends on your use-case.

-- 
Chris Horrocks

From: Jason J. W. Williams <jasonjwwilliams@gmail.com>
Reply: user@flume.apache.org <user@flume.apache.org>
Date: 7 June 2016 at 19:03:59
To: user@flume.apache.org <user@flume.apache.org>
Subject:  Re: Kafka Sink random partition assignment  

Thanks again Chris. I am curious why I see the round-robin behavior I expected when using
kafka-console-producer to inject messages though. 

-J

On Tuesday, June 7, 2016, Chris Horrocks <chris@hor.rocks> wrote:
It's by design of Kafka (and by extension flume). The producers are designed to be many-to-one
(producers to partitions) and as such picking a random partition every 10 minutes prevents
separate producer instances from all randomly picking the same partition. 

-- 
Chris Horrocks

From: Jason Williams <jasonjwwilliams@gmail.com>
Reply: user@flume.apache.org <user@flume.apache.org>
Date: 7 June 2016 at 09:43:34
To: user@flume.apache.org <user@flume.apache.org>
Subject:  Re: Kafka Sink random partition assignment

Hey Chris,

Thanks for help! 

Is that a limitation of the Flume Kafka sink or Kafka itself? Because when I use another Kafka
producer and publish without a key, it randomly moves among the partitions on every publish.

-J

Sent via iPhone

On Jun 7, 2016, at 00:08, Chris Horrocks <chris@hor.rocks> wrote:

The producers bind to random partitions and move every 10 minutes. If you leave it long enough
you should see it in the producer flume agent logs, although there's nothing to stop it from
"randomly" choosing the same partition twice. Annoyingly there's no concept of producer groups
(yet) to ensure that producers apportion the available partitions between them as this would
create a synchronisation issue between what should be entirely independent processes. 

-- 
Chris Horrocks
On 7 June 2016 at 00:32:29, Jason J. W. Williams (jasonjwwilliams@gmail.com) wrote:

Hi,

New to flume and I'm trying to relay log messages received over netcat source to Kafka sink. 

Everything seems to be fine, except that Flume is acting like it IS assigning a partition
key to the produced messages though none is assigned. I'd like the messages to be assigned
to a random partition, so that consumers are load balanced.

* Flume 1.6.0
* Kafka 0.9.0.1

Flume config: https://gist.github.com/williamsjj/8ae025906955fbc4b5f990e162b75d7c

Kafka topic config: kafka-topics --zookeeper localhost/kafka --create --topic activity.history
--partitions 20 --replication-factor 1

Python consumer program: https://gist.github.com/williamsjj/9e67287f0154816c3a733a39ad008437

Test program (publishes to Flume): https://gist.github.com/williamsjj/1eb097a187a3edb17ec1a3913e47e58b

Flume agent listens on 3132tcp for connections, and publishes messages received to the Kafka
activity.history topic.  I'm running two instances of the Python consumer.

What happens however, is all logs messages get sent to a single Kafka consumer...if I restart
Flume (leave consumers running) and re-run the test, all messages get published to the other
consumer. So it feels like Flume is assigning a permanent partition key even though one is
not defined (and should therefore be random).

Any advice is greatly appreciated.

-J
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