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https://issues.apache.org/jira/browse/KAFKA-3959?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15662738#comment-15662738
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Ewen Cheslack-Postava commented on KAFKA-3959:
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[~granthenke] [~onurkaraman] [~toddpalino] Any more thoughts on this? I think
the main use case for handling < 3 brokers by default is when we start up a
"cluster" locally for test purposes. Any real use case that wanted a lower
replication factor could set it explicitly. This is pretty important and we
don't really want to have users jump through hoops to do so; that said, a
dramatic warning wouldn't be the end of the world. Maybe even some combination
of a low setting plus a setting that gives unsafe warnings but allows unsafely
low replication factors for this topic?
> __consumer_offsets wrong number of replicas at startup
> ------------------------------------------------------
>
> Key: KAFKA-3959
> URL: https://issues.apache.org/jira/browse/KAFKA-3959
> Project: Kafka
> Issue Type: Bug
> Components: consumer, offset manager, replication
> Affects Versions: 0.9.0.1, 0.10.0.0
> Environment: Brokers of 3 kafka nodes running Red Hat Enterprise
> Linux Server release 7.2 (Maipo)
> Reporter: Alban Hurtaud
>
> When creating a stack of 3 kafka brokers, the consumer is starting faster
> than kafka nodes and when trying to read a topic, only one kafka node is
> available.
> So the __consumer_offsets is created with a replication factor set to 1
> (instead of configured 3) :
> offsets.topic.replication.factor=3
> default.replication.factor=3
> min.insync.replicas=2
> Then, other kafka nodes go up and we have exceptions because the replicas #
> for __consumer_offsets is 1 and min insync is 2. So exceptions are thrown.
> What I missed is : Why the __consumer_offsets is created with replication to
> 1 (when 1 broker is running) whereas in server.properties it is set to 3 ?
> To reproduce :
> - Prepare 3 kafka nodes with the 3 lines above added to servers.properties.
> - Run one kafka,
> - Run one consumer (the __consumer_offsets is created with replicas =1)
> - Run 2 more kafka nodes
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