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From David Garcia <dav...@spiceworks.com>
Subject Re: Same leader for all partitions for topics
Date Fri, 07 Oct 2016 16:22:15 GMT
Maybe someone already answered this…but you can use the repartitioner to fix that (it’s
included with Kafka)

As far as root cause, you probably had a few leader elections due to excessive latency.  There
is a cascading scenario that I noticed Kafka is vulnerable to.  The events transpire as follows:

1.) network latency occurs due to Random acts of God.
2.) This triggers leader election for some partitions.
3.) Because the new leaders now have more work to do, this may introduce more latency which
will trigger more leader elections…wash and repeat.
4.) Now we have one ring to rule them…one ring to find them, one ring to bring them all
and in the darkness bind them.

I’m not sure how much new leader election would trigger disk reads (possibly because the
leader may not have the newly served data in the OS disk cache)…but that may be a source
for more latency (perhaps a more learned voice can chime in here)

In any case, you should probably have some kind of alerting on leadership distribution.  And
hedge against this scenario with beefy machines. 


On 10/7/16, 2:49 AM, "Misra, Rahul" <Rahul.Misra@altisource.com> wrote:

    I have been using a 3 node kafka cluster for development for some time now. I have created
some topics on this cluster. Yesterday I observed the following when I used 'describe' for
the topics:
    The Kafka version I'm using is: 9.0.1 (kafka_2.11-
    Topic:topicIc  PartitionCount:3        ReplicationFactor:3     Configs:
            Topic: topicIc Partition: 0    Leader: 0       Replicas: 1,2,0 Isr: 0,2,1
            Topic: topicIc Partition: 1    Leader: 0       Replicas: 2,0,1 Isr: 0,2,1
            Topic: topicIc Partition: 2    Leader: 0       Replicas: 0,1,2 Isr: 2,0,1
    Topic:topicR   PartitionCount:3        ReplicationFactor:3     Configs:
            Topic: topicR  Partition: 0    Leader: 0       Replicas: 0,1,2 Isr: 2,0,1
            Topic: topicR  Partition: 1    Leader: 0       Replicas: 1,2,0 Isr: 0,2,1
            Topic: topicR  Partition: 2    Leader: 0       Replicas: 2,0,1 Isr: 0,2,1
    Topic:topicSubE        PartitionCount:1        ReplicationFactor:3     Configs:
            Topic: topicSubE       Partition: 0    Leader: 0       Replicas: 0,2,1 Isr: 0,2,1
    Topic:topicSubIc       PartitionCount:1        ReplicationFactor:3     Configs:
            Topic: topicSubIc      Partition: 0    Leader: 0       Replicas: 2,0,1 Isr: 0,2,1
    Topic:topicSubLr       PartitionCount:1        ReplicationFactor:3     Configs:
            Topic: topicSubLr      Partition: 0    Leader: 0       Replicas: 0,1,2 Isr: 2,0,1
    Topic:topicSubR        PartitionCount:1        ReplicationFactor:3     Configs:
            Topic: topicSubR       Partition: 0    Leader: 0       Replicas: 0,1,2 Isr: 2,0,1
    As you would observe, the leader for all the partitions for all the topics is just one
node: Broker node 0. This is true even for the '__consumer_offsets' topic.
    The brokers are up and running on all the 3 nodes and the Zookeeper nodes are also running
    Does anybody have any ideas as to why this may have happened?
    Is there a way to manually trigger rebalance of partitions to the nodes?
    Rahul Misra
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