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https://issues.apache.org/jira/browse/KAFKA-1510?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14075447#comment-14075447
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nicu marasoiu commented on KAFKA-1510:
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Hi,
I am confused. Let me state some understandings and check which is ok and which 
not.

So the migration of offsets from zk to kafka is to : set dual commit, leave 
storage to zookeeper, wait for kafka to be copied on the offset commits, and 
switch storage to kafka, yes?

So currently kafka is copied with the offsets only when data flows, and for the 
purpose of this task, we need to add one or 2 more cases when it is getting the 
offset: when shutting down, or perhaps periodically.

So this task applies only when storage==kafka and dualCommit ==true, right?

I would first ask why the write to zookeeper the new offsets, only if the write 
to kafka was ok? 

I would write both directions at all time, and perhaps keep 2 checkpoint 
structures, one kafka one zookeeper.

So if I presume correctly, the first phrase in the task description I don't 
think "in addition to setting offsets.storage to kafka" is correct, because 
logically, unless there is a tool to copy offsets, you first set dual, wait for 
offsets to sync and for all clients to reboot in dual and sync, then switch 
storage to kafka (so it is not at the same time like the description suggests), 
and then reboot clients in single kafka mode, yes?

Waiting for clarifications, I've started coding, but it is better I fully 
understand first.

> Force offset commits when migrating consumer offsets from zookeeper to kafka
> ----------------------------------------------------------------------------
>
>                 Key: KAFKA-1510
>                 URL: https://issues.apache.org/jira/browse/KAFKA-1510
>             Project: Kafka
>          Issue Type: Bug
>    Affects Versions: 0.8.2
>            Reporter: Joel Koshy
>            Assignee: nicu marasoiu
>              Labels: newbie
>             Fix For: 0.8.2
>
>
> When migrating consumer offsets from ZooKeeper to kafka, we have to turn on 
> dual-commit (i.e., the consumers will commit offsets to both zookeeper and 
> kafka) in addition to setting offsets.storage to kafka. However, when we 
> commit offsets we only commit offsets if they have changed (since the last 
> commit). For low-volume topics or for topics that receive data in bursts 
> offsets may not move for a long period of time. Therefore we may want to 
> force the commit (even if offsets have not changed) when migrating (i.e., 
> when dual-commit is enabled) - we can add a minimum interval threshold (say 
> force commit after every 10 auto-commits) as well as on rebalance and 
> shutdown.
> Also, I think it is safe to switch the default for offsets.storage from 
> zookeeper to kafka and set the default to dual-commit (for people who have 
> not migrated yet). We have deployed this to the largest consumers at linkedin 
> and have not seen any issues so far (except for the migration caveat that 
> this jira will resolve).



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