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https://issues.apache.org/jira/browse/KAFKA-5794?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16168737#comment-16168737
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Apurva Mehta commented on KAFKA-5794:
-------------------------------------
Bumping this to a future release, we will just add the message format version
to the {{TopicMetadata}} returned in {{MetadatResponse}} for this release. This
will be tracked separately.
> Introduce new idempotence mode to gracefully deal with topics on the older
> message format
> -----------------------------------------------------------------------------------------
>
> Key: KAFKA-5794
> URL: https://issues.apache.org/jira/browse/KAFKA-5794
> Project: Kafka
> Issue Type: Sub-task
> Affects Versions: 0.11.0.0
> Reporter: Apurva Mehta
> Assignee: Apurva Mehta
>
> In the discussion of KIP-185: Make exactly once in order delivery per
> partition the default producer setting, it was realized that we don't have
> graceful handling when an idempotence-enabled producer is writing to a broker
> with a message format older than v2 (ie. the 0.11.0 message format).
> In particular, if we enable idempotence, any produce requests to topics with
> an older message format will fail with an UnsupportedVersionException. Thus
> if the idempotent producer was to be made the default, the out of the box
> producer would fail to produce when used with clusters which haven't upgraded
> the message format yet.
> This is particularly problematic since the recommended upgrade path is to
> upgrade broker code while keeping the message format at the older version,
> then upgrade all clients, and only finally upgrade the message format on the
> server. With the current behavior, the middle step is actually untenable if
> we enable idempotence as the default.
> More details available at:
> https://cwiki.apache.org/confluence/display/KAFKA/Kafka+Exactly+Once+-+Dealing+with+older+message+formats+when+idempotence+is+enabled
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