Producing a Kafka message with a Null Value (Tombstone) from the Console

Question

Is there any way to produce a message in the kafka-console-producer with a null value (ie. mark it for the compactor to delete it with a tombstone)?

I've tried producing "mykey" and "mykey|". The former produces an error and the later makes the value the empty string. Running producer like this:

$KAFKA_HOME/bin/kafka-console-producer --broker-list localhost:9092 --topic mytopic --property "parse.key=true" --property "key.separator=|"

Answer 1

Have a look at kafkacat (the netcat of kafka). Quoting the doc:

Produce a tombstone (a "delete" for compacted topics) for key "abc" by providing an empty message value which -Z interpretes as NULL:

echo "abc:" | kafkacat -b mybroker -t mytopic -Z -K:

Answer 2

Unfortunately, there is no way to do that using console-producer

this is a code snippet from ConsoleProducer class (how it reads the data). Kafka 0.11.0 (don't think that it was changed significantly between different versions).

override def readMessage() = {
  lineNumber += 1
  print(">")
  (reader.readLine(), parseKey) match {
    case (null, _) => null
    case (line, true) =>
      line.indexOf(keySeparator) match {
        case -1 =>
          if (ignoreError) new ProducerRecord(topic, line.getBytes(StandardCharsets.UTF_8))
          else throw new KafkaException(s"No key found on line $lineNumber: $line")
        case n =>
          val value = (if (n + keySeparator.size > line.size) "" else line.substring(n + keySeparator.size)).getBytes(StandardCharsets.UTF_8)
          new ProducerRecord(topic, line.substring(0, n).getBytes(StandardCharsets.UTF_8), value)
      }
    case (line, false) =>
      new ProducerRecord(topic, line.getBytes(StandardCharsets.UTF_8))
  }
}

as you can see, the value is always an non-nullable array of bytes