[jira] [Commented] (KAFKA-3561) Auto create through topic for KStream aggregation and join

["Damian Guy (JIRA)" <ji...@apache.org>]

    [ https://issues.apache.org/jira/browse/KAFKA-3561?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15303877#comment-15303877 ] 

Damian Guy commented on KAFKA-3561:
-----------------------------------

Guozhang - i'd like to do this if it is ok with you. I'm going to need a bit of guidance though.
It looks to me that I'd need to change the signature of map to something like:

 {code}
<K1, V1> KStream<K1, V1> map(final KeyValueMapper<K, V, KeyValue<K1, V1>> mapper,
                                 final Serde<K1> keySerde,
                                 final Serde<V1> valueSerde,
                                 final String topic);
{code}

and then it could be implemented like so:
{code}
@Override
    public <K1, V1> KStream<K1, V1> map(final KeyValueMapper<K, V, KeyValue<K1, V1>> mapper,
                                        final Serde<K1> keySerde,
                                        final Serde<V1> valueSerde,
                                        final String topic) {
        String name = topology.newName(MAP_NAME);
        topology.addProcessor(name, new KStreamMap<>(mapper), this.name);
        return new KStreamImpl<K1, V1>(topology, name, null).through(keySerde, valueSerde, topic);
    }
{code}

What other methods does this apply to. What am I missing? (I'm sure there is a lot of context i'm missing)
Thanks,
Damian

> Auto create through topic for KStream aggregation and join
> ----------------------------------------------------------
>
>                 Key: KAFKA-3561
>                 URL: https://issues.apache.org/jira/browse/KAFKA-3561
>             Project: Kafka
>          Issue Type: Bug
>          Components: streams
>            Reporter: Guozhang Wang
>            Assignee: Damian Guy
>              Labels: api
>             Fix For: 0.10.1.0
>
>
> For KStream.join / aggregateByKey operations that requires the streams to be partitioned on the record key, today users should repartition themselves through the "through" call:
> {code}
> stream1 = builder.stream("topic1");
> stream2 = builder.stream("topic2");
> stream3 = stream1.map(/* set the right key for join*/).through("topic3");
> stream4 = stream2.map(/* set the right key for join*/).through("topic4");
> stream3.join(stream4, ..)
> {code}
> This pattern can actually be done by the Streams DSL itself instead of requiring users to specify themselves, i.e. users can just set the right key like (see KAFKA-3430) and then call join, which will be translated by adding the "internal topic for repartition".
> Another thing is that today if user do not call "through" after setting a new key, the aggregation result would not be correct as the aggregation is based on key B while the source partitions is partitioned by key A and hence each task will only get a partial aggregation for all keys. But this is not validated in the DSL today. We should do both the auto-translation and validation.



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