KafkaStream.KTable如何以（緊湊的）KV樣式將數據寫入kafka主題

Question

在Kafka（0.11.0.1）Streams中，一個演示應用程序與Streams應用程序一起玩

// Serializers/deserializers (serde) for String and Long types
final Serde<String> stringSerde = Serdes.String();
final Serde<Long> longSerde = Serdes.Long();

// Construct a `KStream` from the input topic "streams-plaintext-input", where message values
// represent lines of text (for the sake of this example, we ignore whatever may be stored
// in the message keys).
KStream<String, String> textLines = builder.stream(stringSerde, stringSerde, "streams-plaintext-input");

KTable<String, Long> wordCounts = textLines
    // Split each text line, by whitespace, into words.
    .flatMapValues(value -> Arrays.asList(value.toLowerCase().split("\\W+")))

    // Group the text words as message keys
    .groupBy((key, value) -> value)

    // Count the occurrences of each word (message key).
    .count("Counts")

    // Store the running counts as a changelog stream to the output topic.
    wordCounts.to(stringSerde, longSerde, "streams-wordcount-output");

第5步，在處理了一些數據之后，我們可以在接收器主題streams-wordcount-output中看到壓縮的KV對（例如stream 2 ），

> bin/kafka-console-consumer.sh --bootstrap-server localhost:9092
    --topic streams-wordcount-output \
    --from-beginning \
    --formatter kafka.tools.DefaultMessageFormatter \
    --property print.key=true \
    --property print.value=true \
    --property key.deserializer=org.apache.kafka.common.serialization.StringDeserializer \
    --property value.deserializer=org.apache.kafka.common.serialization.LongDeserializer 

all     1 
streams 1 
lead    1 
to      1 
kafka   1 
hello   1 
kafka   2 
streams 2

問題是上述數據中的KTable wordCounts如何以鍵值樣式將數據寫入主題流-wordcount-output ？

主題streams-wordcount-output的選項cleanup.policy似乎是默認值delete ，而不是compact （通過bin / kafka-configs.sh）

Answer 1

所有輸入和輸出主題都在Kafka Streams的“范圍之外”。 創建和配置這些主題是用戶的責任。

因此，您的主題"streams-wordcount-output"將具有您在創建主題時指定的配置。

比照 https://docs.confluent.io/current/streams/developer-guide.html#managing-topics-of-a-kafka-streams-application