Jason Gustafson created KAFKA-6794:
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Summary: Support for incremental replica reassignment
Key: KAFKA-6794
URL: https://issues.apache.org/jira/browse/KAFKA-6794
Project: Kafka
Issue Type: Improvement
Reporter: Jason Gustafson
Say you have a replication factor of 4 and you trigger a reassignment which
moves all replicas to new brokers. Now 8 replicas are fetching at the same time
which means you need to account for 8 times the current load plus the catch-up
replication. To make matters worse, the replicas won't all become in-sync at
the same time; in the worst case, you could have 7 replicas in-sync while one
is still catching up. Currently, the old replicas won't be disabled until all
new replicas are in-sync. This makes configuring the throttle tricky since ISR
traffic is not subject to it.
Rather than trying to bring all 4 new replicas online at the same time, a
friendlier approach would be to do it incrementally: bring one replica online,
bring it in-sync, then remove one of the old replicas. Repeat until all
replicas have been changed. This would reduce the impact of a reassignment and
make configuring the throttle easier at the cost of a slower overall
reassignment.
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