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From Andrew Coates <big.andy.coa...@gmail.com>
Subject Re: Does Kafka connector leverage Kafka message keys?
Date Wed, 13 Apr 2016 07:20:35 GMT
Hi Stephan,

If we were to do that, would flink leverage the fact that Kafka has already
partitioned the data by the key, or would flink attempt to shuffle the data
again into its own partitions, potentially shuffling data between machines
for no gain?



On Sun, 10 Apr 2016, 13:22 Stephan Ewen, <sewen@apache.org> wrote:

> Hi!
> You are right with your observations. Right now, you would have to create
> a "Tuple2<Key, Value>" in the KeyedDeserializationSchema. That is what also
> a KeyedStream holds internally.
> A KeyedStream in Flink is more than just a stream that has a Key and a
> Value - it is also partitioned by the key, and Flink maintains track of
> keyed state in those streams. That's why it has to be explicitly created.
> For convenience, one could make an addition that FlinkKafkaConsumer can
> accept two DeserializationSchema (one for key, one for value) and return a
> Tuple2<Key, Value> automatically.
> Greetings,
> Stephan
> On Sun, Apr 10, 2016 at 5:49 AM, Elias Levy <fearsome.lucidity@gmail.com>
> wrote:
>> I am wondering if the Kafka connectors leverage Kafka message keys at all?
>> Looking through the docs my impression is that it does not.  E.g. if I
>> use the connector to consume from a partitioned Kafka topic, what I will
>> get back is a DataStream, rather than a KeyedStream.  And if I want access
>> to a message's key the key must be within the message to extract it or I
>> have to make use of a KeyedDeserializationSchema with the connector to
>> access the Kafka message key and insert it into the type returned by the
>> connector.
>> Similar, it would seem that you have give the Kafka product sink a
>> KeyedSerializationSchema, which will obtain a Kafka key and a Kafka message
>> from the events from a DataStream, but you can product from a KeyedStream
>> where the key if obtained from the stream itself.
>> Is this correct?

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