Where exactly is the default partition decided in kafka producer?

Question

I am trying to grep through source code and all I am able to find is

/Users/myUser/.m2/repository/org/apache/kafka/kafka_2.10/0.9.0.2/kafka_2.10-0.9.0.2.jar!/kafka/javaapi/producer/Producer.class

public void send(List<KeyedMessage<K, V>> messages) {
   this.underlying().send(scala.collection.JavaConversions..MODULE$.asScalaBuffer(messages).toSeq());
}

which calls

/Users/myUser/.m2/repository/org/apache/kafka/kafka_2.10/0.9.0.2/kafka_2.10-0.9.0.2.jar!/kafka/producer/Producer.class

public void send(Seq<KeyedMessage<K, V>> messages) {
    synchronized(this.lock()) {
        if(this.hasShutdown().get()) {
            throw new ProducerClosedException();
        } else {
            this.recordStats(messages);
            boolean var3 = this.sync();
            BoxedUnit var4;
            if(var3) {
                this.eventHandler().handle(messages);
                var4 = BoxedUnit.UNIT;
            } else {
                if(var3) {
                    throw new MatchError(BoxesRunTime.boxToBoolean(var3));
                }

                this.asyncSend(messages);
                var4 = BoxedUnit.UNIT;
            }

            BoxedUnit var10000 = BoxedUnit.UNIT;
        }
    }
}

Its quite confusing because I am expecting both the send function to accept partition id from default partition like

public void send(List<KeyedMessage<K, V>> messages, int partition id)

or somehow call the default partition to get the partition id in the send method definition

But I don't see the partition id used anywhere.

Can someone point me a direction on where to look for where the partition is decided?

Is it before we call producer.send ?

Answer 1

You're looking at the old API, that logic is in the EventHandler , which is called by the send method

---

For the newer clients, you can see it in the doSend method

 int partition = partition(record, serializedKey, serializedValue, cluster);
 tp = new TopicPartition(record.topic(), partition);

The partitioner class is loaded from the properties given to the Producer . If not defined, it's the default