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From Josh Foure <user...@yahoo.com>
Subject Re: Partitions and highlevel consumers
Date Tue, 02 Jul 2013 19:34:43 GMT
Hi, am a also new to Kafka but let me explain my understanding which someone with more knowledge
can confirm.  There are actually 2 scenarios:

1.  If all 5 of your consumers are in different "consumer groups" then this will behave like
a JMS topic where all 5 of your consumers will each get a copy of all of the messages.  You
can add as many consumers as you want regardless of the fact that there is only 1 partition.

2.  If all 5 of your consumers are in the same "consumer group" and there is only 1 partition,
only 1 consumer will get a copy of the messages.  You should increase your number of partitions
so there are as many as there are consumers in this case so each will get 1/5 of the messages
(assuming the messages are evenly distributed across the partitions).

Is that what you were looking for?  Can someone confirm that what I stated is accurate?


 From: Vinicius Carvalho <viniciusccarvalho@gmail.com>
To: users@kafka.apache.org 
Sent: Tuesday, July 2, 2013 2:55 PM
Subject: Partitions and highlevel consumers

Hi guys, we are starting with kafka in our project. We are using version
0.8. I come from a traditional JMS MoM architecture, and some things are
new to me.

One thing that I'm not getting is the mapping between partitions and number
of threads. On a single consumer I can see the relationship but what
happens when you have multiple consumers?

So say, I have a topic and I have 5 instances of services that acts as
consumers. On a traditional pub/sub I would have all 5 instances to consume
the message right? Even if this topic only has one partition and now we
have 5 threads (one per jvm instance) consuming it. Does this proceed?

Just want to make sure if that is the expected behavior, from the docs it
wasn't clear if its the number of threads per consumer, or the total number
of threads around all clients to the topic.


The intuitive mind is a sacred gift and the
rational mind is a faithful servant. We have
created a society that honors the servant and
has forgotten the gift.
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