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https://issues.apache.org/jira/browse/KAFKA-4682?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16113290#comment-16113290
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Vahid Hashemian commented on KAFKA-4682:
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[~hachikuji] et al.
I'm interested in taking this on. Just to make sure I understand the proper
approach (KIP) before starting to write the draft:
We don't want to expire group offsets while the group is active, so we would
want to phase out individual offset expirations inside the group (that would
mean removing the unused retention time field from the OffsetCommit protocol).
On the other hand, we seem to now need some sort of an expiration time per
consumer group so we can remove offsets within the group if that expiration
time is passed and the group is no longer active. This expiration time is set
and takes effect only when the group becomes empty.
Is this a reasonable summary of what needs to happen?
> Committed offsets should not be deleted if a consumer is still active
> ---------------------------------------------------------------------
>
> Key: KAFKA-4682
> URL: https://issues.apache.org/jira/browse/KAFKA-4682
> Project: Kafka
> Issue Type: Bug
> Reporter: James Cheng
>
> Kafka will delete committed offsets that are older than
> offsets.retention.minutes
> If there is an active consumer on a low traffic partition, it is possible
> that Kafka will delete the committed offset for that consumer. Once the
> offset is deleted, a restart or a rebalance of that consumer will cause the
> consumer to not find any committed offset and start consuming from
> earliest/latest (depending on auto.offset.reset). I'm not sure, but a broker
> failover might also cause you to start reading from auto.offset.reset (due to
> broker restart, or coordinator failover).
> I think that Kafka should only delete offsets for inactive consumers. The
> timer should only start after a consumer group goes inactive. For example, if
> a consumer group goes inactive, then after 1 week, delete the offsets for
> that consumer group. This is a solution that [~junrao] mentioned in
> https://issues.apache.org/jira/browse/KAFKA-3806?focusedCommentId=15323521&page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel#comment-15323521
> The current workarounds are to:
> # Commit an offset on every partition you own on a regular basis, making sure
> that it is more frequent than offsets.retention.minutes (a broker-side
> setting that a consumer might not be aware of)
> or
> # Turn the value of offsets.retention.minutes up really really high. You have
> to make sure it is higher than any valid low-traffic rate that you want to
> support. For example, if you want to support a topic where someone produces
> once a month, you would have to set offsetes.retention.mintues to 1 month.
> or
> # Turn on enable.auto.commit (this is essentially #1, but easier to
> implement).
> None of these are ideal.
> #1 can be spammy. It requires your consumers know something about how the
> brokers are configured. Sometimes it is out of your control. Mirrormaker, for
> example, only commits offsets on partitions where it receives data. And it is
> duplication that you need to put into all of your consumers.
> #2 has disk-space impact on the broker (in __consumer_offsets) as well as
> memory-size on the broker (to answer OffsetFetch).
> #3 I think has the potential for message loss (the consumer might commit on
> messages that are not yet fully processed)
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