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From Ye Hong <Ye.H...@audiencescience.com>
Subject Partition reassignment causes replica number and Isr to go above configured value
Date Wed, 05 Aug 2015 21:55:28 GMT
Hi All,

We recently performed a partition reassignment on one of our Kafka cluster. (0.8.1.1, all
topics configured to have 2 replicas.)

After the completion of reassignment, we have noticed that some of the partitions has 3 replicas
and 3 Isrs instead of 2. 

for example:
    Topic: topic1    Partition: 7    Leader: 5    Replicas: 5,2    Isr: 5,2  (correct number
of replicas and Isr)
    Topic: topic1    Partition: 8    Leader: 6    Replicas: 6,4,2    Isr: 6,4,2  (has more
replica and Isr than configured)
    Topic: topic1    Partition: 32    Leader: 5    Replicas: 5,4,2    Isr: 5,4,2

Previously, we have seen 3 replicas during the reassignment, however, the Isr count was always
2, and replica count will drop back to 2 after the completion of reassignment. 

Just wonder if someone has encountered similar issue. What would be a good way to fix it?
I am thinking about triggering a partial partition reassignment with a manually created partition
assignment config that would bring the replicas back to 2. Is this the right way to fix such
issue?

Thanks,

Ye

P.S.
Here are the step we did for the reassignment:
1. /usr/local/kafka/bin/kafka-reassign-partitions.sh --zookeeper <zookeeper_host_name>:<port>
--broker-list "<broker_list>" --generate --topics-to-move-json-file <topics-to-move_json_file>
2. From the console output, copy the second part and put it into a text file assignment_json_file.
3. /usr/local/kafka/bin/kafka-reassign-partitions.sh --zookeeper <zookeeper_host_name>:<port>
--broker-list "<broker_list>" --execute --topics-to-move-json-file <topics-to-move_json_file>
--reassignment-json-file <assignment_json_file>
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