The imbalance is measured wrt preferred leaders. i.e., for every partition, the first replica in the assigned replica list (as shown in the output of kafka-topics.sh) is called the preferred replica. On each broker, the auto-balancer counts the number of partitions led by that broker for which the preferred leader is on another broker. If it exceeds the thresholds it does a preferred replica leader election.
In your case, can you run the kafka-topics.sh script and see if the preferred replicas are evenly distributed? Also, which version of Kafka are you using? Thanks, Joel On Tue, Nov 18, 2014 at 11:48:35AM -0500, Wes Chow wrote: > I'm trying to understand the config options for auto-rebalancing. > This is what we have in /etc/kafka/server.properties for all the > nodes: > > auto.leader.rebalance.enable=true > leader.imbalance.per.broker.percentage=10 > leader.imbalance.check.interval.seconds=300 > > We have 10 nodes for this topic which has 512 partitions. They were > evenly balanced before I started my experiment. I shut down two of > the nodes, and the number of leaders per node is now: > > 75 10 > 68 3 > 57 4 > 67 5 > 57 6 > 68 7 > 63 8 > 57 9 > > Where the first column is # of leaders, and the second column is > node #. You can see that nodes 1 and 2 have no leaders, since > they're down. It's been about half an hour since I did this and the > balancing hasn't changed. > > The documentation on the config option is very ambiguous. My > interpretation is that it says if any particular node has 10% more > leaders then auto-rebalance kicks in. If that means 10% more than > the average, then node #10 has 75 partitioners, and the average is > 64, so that's a 17% difference. > > So I think I'm misunderstanding either what auto-rebalance is > supposed to do or the condition that's supposed to trigger it. Any > clues? > > Thanks, > Wes >
