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https://issues.apache.org/jira/browse/KAFKA-4084?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16648581#comment-16648581
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Jiaxin YE commented on KAFKA-4084:
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Is this issue really resolved? I am using Kafka 1.1.0 and my cluster with 97
hosts and 22,500 partitions face the same problem. Here is what I see in the
log for one partition.
1. Broker A went offline for some reasons (deployment, network glitch .. ect)
2. Controller elected broker B as the leader for that partition and let B
become the leader.
3. Broker A went online again.
4. Controller let A become the follower of broker B and A is in sync with
broker B.
5. Controller triggered auto rebalance and elect A as the new leader and inform
B to become the follower.
6. Broker B became the follower and then Controller informed A to be the leader.
7. Broker A became the leader.
The problem is the broker A has 100% CPU utilization on step 6 and takes a long
to for it to handle the controller request to become a leader. There a great
latency between 6 and 7 which cause a partition to live without a leader for
around 1- 30 minutes.
> automated leader rebalance causes replication downtime for clusters with too
> many partitions
> --------------------------------------------------------------------------------------------
>
> Key: KAFKA-4084
> URL: https://issues.apache.org/jira/browse/KAFKA-4084
> Project: Kafka
> Issue Type: Bug
> Components: controller
> Affects Versions: 0.8.2.2, 0.9.0.0, 0.9.0.1, 0.10.0.0, 0.10.0.1
> Reporter: Tom Crayford
> Priority: Major
> Labels: reliability
> Fix For: 1.1.0
>
>
> If you enable {{auto.leader.rebalance.enable}} (which is on by default), and
> you have a cluster with many partitions, there is a severe amount of
> replication downtime following a restart. This causes
> `UnderReplicatedPartitions` to fire, and replication is paused.
> This is because the current automated leader rebalance mechanism changes
> leaders for *all* imbalanced partitions at once, instead of doing it
> gradually. This effectively stops all replica fetchers in the cluster
> (assuming there are enough imbalanced partitions), and restarts them. This
> can take minutes on busy clusters, during which no replication is happening
> and user data is at risk. Clients with {{acks=-1}} also see issues at this
> time, because replication is effectively stalled.
> To quote Todd Palino from the mailing list:
> bq. There is an admin CLI command to trigger the preferred replica election
> manually. There is also a broker configuration “auto.leader.rebalance.enable”
> which you can set to have the broker automatically perform the PLE when
> needed. DO NOT USE THIS OPTION. There are serious performance issues when
> doing so, especially on larger clusters. It needs some development work that
> has not been fully identified yet.
> This setting is extremely useful for smaller clusters, but with high
> partition counts causes the huge issues stated above.
> One potential fix could be adding a new configuration for the number of
> partitions to do automated leader rebalancing for at once, and *stop* once
> that number of leader rebalances are in flight, until they're done. There may
> be better mechanisms, and I'd love to hear if anybody has any ideas.
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