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https://issues.apache.org/jira/browse/KAFKA-3401?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15195218#comment-15195218
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Ismael Juma commented on KAFKA-3401:
------------------------------------
[~becket_qin], the upgrade notes say:
{code}
<b>Note:</b> By setting the message format version, one certifies that all
existing messages are on or below that
message format version. Otherwise consumers before 0.10.0.0 might break. In
particular, after the message format
is set to 0.10.0, one should not change it back to an earlier format as it
may break consumers on versions before 0.10.0.0.
{code}
So, did you really mean that we should do step 4 in KAFKA-3202?
{code}
4. change the message format version for both topic back to 0.9.0 on the fly.
{code}
Or do we need to switch off older clients before we do that (under the
assumption that the upgrade notes are correct)?
> Message format change on the fly breaks 0.9 consumer
> ----------------------------------------------------
>
> Key: KAFKA-3401
> URL: https://issues.apache.org/jira/browse/KAFKA-3401
> Project: Kafka
> Issue Type: Bug
> Affects Versions: 0.10.0.0
> Reporter: Eno Thereska
> Assignee: Jiangjie Qin
> Priority: Blocker
> Fix For: 0.10.0.0
>
> Attachments: 2016-03-15--009.zip
>
>
> The new system test as part of KAFKA-3202 reveals a problem when the message
> format is changed on the fly. When the cluster is using 0.10.x brokers and
> producers and consumers use version 0.9.0.1 an error happens when the message
> format is changed on the fly to version 0.9:
> {code}
> Exception: {'ConsoleConsumer-worker-1': Exception('Unexpected message format
> (expected an integer). Message: null',)}
> {code}
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