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https://issues.apache.org/jira/browse/KAFKA-2260?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16505891#comment-16505891
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Sven Linstaedt commented on KAFKA-2260:
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Is there a chance for this proposal being scheduled with Kafka 2.0? Or asking
the other way round: What is needed for this KIP being included in the next
release?
> Allow specifying expected offset on produce
> -------------------------------------------
>
> Key: KAFKA-2260
> URL: https://issues.apache.org/jira/browse/KAFKA-2260
> Project: Kafka
> Issue Type: Improvement
> Reporter: Ben Kirwin
> Priority: Minor
> Attachments: KAFKA-2260.patch, expected-offsets.patch
>
>
> I'd like to propose a change that adds a simple CAS-like mechanism to the
> Kafka producer. This update has a small footprint, but enables a bunch of
> interesting uses in stream processing or as a commit log for process state.
> h4. Proposed Change
> In short:
> - Allow the user to attach a specific offset to each message produced.
> - The server assigns offsets to messages in the usual way. However, if the
> expected offset doesn't match the actual offset, the server should fail the
> produce request instead of completing the write.
> This is a form of optimistic concurrency control, like the ubiquitous
> check-and-set -- but instead of checking the current value of some state, it
> checks the current offset of the log.
> h4. Motivation
> Much like check-and-set, this feature is only useful when there's very low
> contention. Happily, when Kafka is used as a commit log or as a
> stream-processing transport, it's common to have just one producer (or a
> small number) for a given partition -- and in many of these cases, predicting
> offsets turns out to be quite useful.
> - We get the same benefits as the 'idempotent producer' proposal: a producer
> can retry a write indefinitely and be sure that at most one of those attempts
> will succeed; and if two producers accidentally write to the end of the
> partition at once, we can be certain that at least one of them will fail.
> - It's possible to 'bulk load' Kafka this way -- you can write a list of n
> messages consecutively to a partition, even if the list is much larger than
> the buffer size or the producer has to be restarted.
> - If a process is using Kafka as a commit log -- reading from a partition to
> bootstrap, then writing any updates to that same partition -- it can be sure
> that it's seen all of the messages in that partition at the moment it does
> its first (successful) write.
> There's a bunch of other similar use-cases here, but they all have roughly
> the same flavour.
> h4. Implementation
> The major advantage of this proposal over other suggested transaction /
> idempotency mechanisms is its minimality: it gives the 'obvious' meaning to a
> currently-unused field, adds no new APIs, and requires very little new code
> or additional work from the server.
> - Produced messages already carry an offset field, which is currently ignored
> by the server. This field could be used for the 'expected offset', with a
> sigil value for the current behaviour. (-1 is a natural choice, since it's
> already used to mean 'next available offset'.)
> - We'd need a new error and error code for a 'CAS failure'.
> - The server assigns offsets to produced messages in
> {{ByteBufferMessageSet.validateMessagesAndAssignOffsets}}. After this
> changed, this method would assign offsets in the same way -- but if they
> don't match the offset in the message, we'd return an error instead of
> completing the write.
> - To avoid breaking existing clients, this behaviour would need to live
> behind some config flag. (Possibly global, but probably more useful
> per-topic?)
> I understand all this is unsolicited and possibly strange: happy to answer
> questions, and if this seems interesting, I'd be glad to flesh this out into
> a full KIP or patch. (And apologies if this is the wrong venue for this sort
> of thing!)
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