Ben Stopford created KAFKA-3438:
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Summary: Rack Aware Replica Reassignment should warn of overloaded
brokers
Key: KAFKA-3438
URL: https://issues.apache.org/jira/browse/KAFKA-3438
Project: Kafka
Issue Type: Improvement
Reporter: Ben Stopford
We've changed the replica reassignment code to be rack aware.
One problem that might catch users out would be that they rebalance the cluster
using kafka-reassign-partitions.sh but their rack configuration means that some
high proportion of replicas are pushed onto a single, or small number of,
brokers.
This should be an easy problem to avoid, by changing the rack assignment
information, but we should probably warn users if they are going to create
something that is unbalanced.
So imagine I have a Kafka cluster of 12 nodes spread over two racks with rack
awareness enabled. If I add a 13th machine, on a new rack, and run the
rebalance tool, that new machine will get ~6x as many replicas as the least
loaded broker.
Suggest a warning be added to the tool output when --generate is called. "The
most loaded broker has 2.3x as many replicas as the the least loaded broker.
This is likely due to an uneven distribution of brokers across racks. You're
advised to alter the rack config so there are approximately the same number of
brokers per rack" and displays the individual rack→#brokers and
broker→#replicas data for the proposed move.
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