[jira] [Commented] (KAFKA-4852) ByteBufferSerializer not compatible with offsets

["Matthias J. Sax (Jira)" <ji...@apache.org>]

    [ https://issues.apache.org/jira/browse/KAFKA-4852?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17778727#comment-17778727 ] 

Matthias J. Sax commented on KAFKA-4852:
----------------------------------------

As reported on https://issues.apache.org/jira/browse/KAFKA-15602, this ticket introduces a couple of breaking changes and bugs.
 # Semantics changes like this, need to be backed up by a KIP
 # The code does not achieve what it aims to do
 # The is lack of proper unit testing

Given that such a change requires a KIP and the current code is broken, we propose to revert this change for the time being, and do a proper fix via a KIP. I prepare a PR for this: [https://github.com/apache/kafka/pull/14617]

\cc [~guozhang] 

> ByteBufferSerializer not compatible with offsets
> ------------------------------------------------
>
>                 Key: KAFKA-4852
>                 URL: https://issues.apache.org/jira/browse/KAFKA-4852
>             Project: Kafka
>          Issue Type: Bug
>          Components: clients
>    Affects Versions: 0.10.1.1
>         Environment: all
>            Reporter: Werner Daehn
>            Assignee: LinShunkang
>            Priority: Minor
>             Fix For: 3.4.0
>
>
> Quick intro: A ByteBuffer.rewind() resets the position to zero. What if the ByteBuffer was created with an offset? new ByteBuffer(data, 3, 10)? The ByteBufferSerializer will send from pos=0 and not from pos=3 onwards.
> Solution: No rewind() but flip() for reading a ByteBuffer. That's what the flip is meant for.
> Story:
> Imagine the incoming data comes from a byte[], e.g. a network stream containing topicname, partition, key, value, ... and you want to create a new ProducerRecord for that. As the constructor of ProducerRecord requires (topic, partition, key, value) you have to copy from above byte[] the key and value. That means there is a memcopy taking place. Since the payload can be potentially large, that introduces a lot of overhead. Twice the memory.
> A nice solution to this problem is to simply wrap the network byte[] into new ByteBuffers:
> ByteBuffer key = ByteBuffer.wrap(data, keystart, keylength);
> ByteBuffer value = ByteBuffer.wrap(data, valuestart, valuelength);
> and then use the ByteBufferSerializer instead of the ByteArraySerializer.
> But that does not work as the ByteBufferSerializer does a rewind(), hence both, key and value, will start at position=0 of the data[].
> public class ByteBufferSerializer implements Serializer<ByteBuffer> {
>     public byte[] serialize(String topic, ByteBuffer data) {
>          data.rewind();



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