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https://issues.apache.org/jira/browse/KAFKA-544?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13502310#comment-13502310
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Joel Koshy commented on KAFKA-544:
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Thanks a lot for addressing the above. Changes look good but for a few typos:
- misspelling (seperat*)
- NewLineMessageFormatter may as well be called DefaultMessageFormatter given
the arbitrary message separator.
- ConsoleProducer - valueEncoderClass should use valueEncoderOpt (line 93).
On null vs. options, I agree that it is cumbersome to use and generally try to
avoid it, but lately I have begun to think it's not too bad especially for
cases like this where it is easy to forget to check for null. E.g., there's if
(xOpt.isDefined) which is only slightly more verbose than if (x != null).
or xOpt.foreach(process(_)) (or map if you need the result) instead of (x !=
null) process(x) removes the need for the isDefined check/match statement and
is not much more verbose.
All that said, you are right that something like this would be caught early on
- so either way works.
> Retain key in producer and expose it in the consumer
> ----------------------------------------------------
>
> Key: KAFKA-544
> URL: https://issues.apache.org/jira/browse/KAFKA-544
> Project: Kafka
> Issue Type: Bug
> Affects Versions: 0.8
> Reporter: Jay Kreps
> Assignee: Jay Kreps
> Priority: Blocker
> Labels: bugs
> Attachments: KAFKA-544-joel-comments.patch, KAFKA-544-v1.patch,
> KAFKA-544-v2.patch, KAFKA-544-v3.patch, KAFKA-544-v4.patch,
> KAFKA-544-v5.patch, KAFKA-544-v6.patch
>
>
> KAFKA-506 added support for retaining a key in the messages, however this
> field is not yet set by the producer.
> The proposal for doing this is to change the producer api to change
> ProducerData to allow only a single key/value pair so it has a one-to-one
> mapping to Message. That is change from
> ProducerData(topic: String, key: K, data: Seq[V])
> to
> ProducerData(topic: String, key: K, data: V)
> The key itself needs to be encoded. There are several ways this could be
> handled. A few of the options:
> 1. Change the Encoder and Decoder to be MessageEncoder and MessageDecoder and
> have them take both a key and value.
> 2. Another option is to change the type of the encoder/decoder to not refer
> to Message so it could be used for both the key and value.
> I favor the second option but am open to feedback.
> One concern with our current approach to serialization as well as both of
> these proposals is that they are inefficient. We go from
> Object=>byte[]=>Message=>MessageSet with a copy at each step. In the case of
> compression there are a bunch of intermediate steps. We could theoretically
> clean this up by instead having an interface for the encoder that was
> something like
> Encoder.writeTo(buffer: ByteBuffer, object: AnyRef)
> and
> Decoder.readFrom(buffer:ByteBuffer): AnyRef
> However there are two problems with this. The first is that we don't actually
> know the size of the data until it is serialized so we can't really allocate
> the bytebuffer properly and might need to resize it. The second is that in
> the case of compression there is a whole other path to consider. Originally I
> thought maybe it would be good to try to fix this, but now I think it should
> be out-of-scope and we should revisit the efficiency issue in a future
> release in conjunction with our internal handling of compression.
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