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https://issues.apache.org/jira/browse/KAFKA-3493?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15227557#comment-15227557
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Maysam Yabandeh commented on KAFKA-3493:
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[~nehanarkhede], git suggests that you have the most recent context about this
function. Could you please chime in?
Thanks.
> Replica fetcher load is not balanced over fetcher threads
> ---------------------------------------------------------
>
> Key: KAFKA-3493
> URL: https://issues.apache.org/jira/browse/KAFKA-3493
> Project: Kafka
> Issue Type: Improvement
> Affects Versions: 0.9.0.1
> Reporter: Maysam Yabandeh
> Fix For: 0.10.0.1
>
>
> The replicas are not evenly distributed among the fetcher threads. This has
> caused some fetcher threads get overloaded and hence their requests time out
> frequently. This is especially a big issue when a new node is added to the
> cluster and the fetch traffic is high.
> Here is an example run in a test cluster with 10 brokers and 6 fetcher
> threads (per source broker). A single topic consisting of 500+ partitions was
> assigned to have a replica for each parition on the newly added broker.
> {code}[kafka-jetstream.canary]myabandeh@sjc8c-rl17-23b:~$ for i in `seq 0 5`;
> do grep ReplicaFetcherThread-$i- /var/log/kafka/server.log | grep "reset its
> fetch offset from 0" | wc -l; done
> 85
> 83
> 85
> 83
> 85
> 85
> [kafka-jetstream.canary]myabandeh@sjc8c-rl17-23b:~$ for i in `seq 0 5`; do
> grep ReplicaFetcherThread-$i-22 /var/log/kafka/server.log | grep "reset its
> fetch offset from 0" | wc -l; done
> 15
> 1
> 13
> 1
> 14
> 1
> {code}
> The problem is that AbstractFetcherManager::getFetcherId method does not take
> the broker id into account:
> {code}
> private def getFetcherId(topic: String, partitionId: Int) : Int = {
> Utils.abs(31 * topic.hashCode() + partitionId) % numFetchers
> }
> {code}
> Hence although the replicas are evenly distributed among the fetcher ids
> across all source brokers, this is not necessarily the case for each broker
> separately.
> I think a random function would do a much better job in distributing the load
> over the fetcher threads from each source broker.
> Thoughts?
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