Nageswara Rao Nageswara Rao - 23 days ago 14
Java Question

Apache Kafka - KafkaStream on topic/partition

I am writing Kafka Consumer for high volume high velocity distributed application. I have only one topic but rate incoming messages is very high. Having multiple partition that serve more consumer would be appropriate for this use-case. Best way to consume is to have multiple stream readers. As per the documentation or available samples, number of KafkaStreams the ConsumerConnector gives out is based on number of topics. Wondering how to get more than one KafkaStream readers [based on the partition], so that I can span one thread per stream or Reading from same KafkaStream in multiple threads would do the concurrent read from multiple partitions?

Any insights are much appreciated.

Answer

Would like to share what I found from mailing list:

The number that you pass in the topic map controls how many streams a topic is divided into. In your case, if you pass in 1, all 10 partitions's data will be fed into 1 stream. If you pass in 2, each of the 2 streams will get data from 5 partitions. If you pass in 11, 10 of them will each get data from 1 partition and 1 stream will get nothing.

Typically, you need to iterate each stream in its own thread. This is because each stream can block forever if there is no new event.

Sample snippet:

topicCount.put(msgTopic, new Integer(partitionCount));
Map<String, List<KafkaStream<byte[], byte[]>>> consumerStreams = connector.createMessageStreams(topicCount);
List<KafkaStream<byte[], byte[]>> streams = consumerStreams.get(msgTopic);

for (final KafkaStream stream : streams) {
    ReadTask task = new ReadTask(stream, msgTopic);
    task.addObserver(this.msgObserver);
    tasks.add(task); executor.submit(task);
}

Reference: http://mail-archives.apache.org/mod_mbox/incubator-kafka-users/201201.mbox/%3CCA+sHyy_Z903dOmnjp7_yYR_aE2sRW-x7XpAnqkmWaP66GOqf6w@mail.gmail.com%3E

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