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This is related to an issue in Kafka 0.7.x (see the discussion in http://apache.markmail.org/thread/c7tdalfketpusqkg). Basically, for a new topic, the producer bootstraps using all existing brokers. However, if a topic already exists on some brokers, the producer never bootstraps again when new brokers are added to the cluster. This means that the producer won't see those new broker. A workaround is to manually create the log directory for that topic on the new brokers.

Why are my brokers

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not

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receiving producer sent messages?

This happened when I tried to enable gzip compression by setting compression.codec to 1. With the code change, I found not a single message was received by the brokers even though I had called producer.send() 1 million times. No error printed by producer and no error could be found in broker's kafka-request.log. By adding log4j.properties to my producer's classpath and switch switching the log level to DEBUG, I captured the java.lang.NoClassDefFoundError: org/xerial/snappy/SnappyInputStream thrown at the producer side. Now I can see this error can be resolved by adding snappy jar to the producer's classpath.

Why is data

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not evenly distributed among partitions when a partitioning key is not specified?

In Kafka producer, a partition key can be specified to indicate the destination partition of the message. By default, a hashing-based partitioner is used to determine the partition id given the key, and people can use customized partitioners also.

To reduce # of open sockets, in 0.8.0 (https://issues.apache.org/jira/browse/KAFKA-1017), when the partitioning key is not specified or null, a producer will pick a random partition and stick to it for some time (default is 10 mins) before switching to another one. So, if there are fewer producers than partitions, at a given point of time, some partitions may not receive any data. To alleviate this problem, one can either reduce the metadata refresh interval or specify a message key and a customized random partitioner. For more detail see this thread http://mail-archives.apache.org/mod_mbox/kafka-dev/201310.mbox/%3CCAFbh0Q0aVh%2Bvqxfy7H-%2BMnRFBt6BnyoZk1LWBoMspwSmTqUKMg%40mail.gmail.com%3E

Is it possible to delete a topic?

In the current version, 0.8.0, no. (You could clear the entire Kafka and zookeeper states to delete all topics and data.) But upcoming releases are expected to include a delete topic tool.

Consumers

Why does my consumer never get any data?

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