Question

我想从KStream实例化一个KTable，并且希望KeyValueStore由Key排序。

我尝试查找KTable API规范（https://kafka.apache.org/20/javadoc/org/apache/kafka/streams/kstream/KTable.html），但是不存在“排序”方法。我还查阅了这篇文章（https://dzone.com/articles/how-to-order-streamed-dataframes），该文章建议通过Processor API实现排序。但是，我正在检查是否可以通过其他方式实现？

Answer 1

使用键将事件添加到StateStore。 StateStore返回的KeyValueIterator以有序方式导航KeyValue。

public class SortProcessor extends AbstractProcessor<String, Event> {

    private static Logger LOG = LoggerFactory.getLogger(SortProcessor.class);
    private final String stateStore;
    private final Long bufferIntervalInSeconds;

    // Why not use a simple Java NavigableMap? Check out my answer at : https://stackoverflow.com/a/62677079/2256618
    private KeyValueStore<String, Event> keyValueStore;

    public SortProcessor(String stateStore, Long bufferIntervalInSeconds) {
        this.stateStore = stateStore;
        this.bufferIntervalInSeconds = bufferIntervalInSeconds;
    }

    @Override
    public void init(ProcessorContext processorContext) {
        super.init(processorContext);
        keyValueStore = (KeyValueStore) context().getStateStore(stateStore);
        context().schedule(Duration.ofSeconds(bufferIntervalInSeconds), PunctuationType.WALL_CLOCK_TIME, this::punctuate);
    }

    void punctuate(long timestamp) {
        LOG.info("Punctuator invoked...");
        try (KeyValueIterator<String, Event> iterator = keyValueStore.all()) {
            while (iterator.hasNext()) {
                KeyValue<String, Event> next = iterator.next();
                if (next.value == null) {
                    continue;
                }
                LOG.info("Sending {}", next.key);
                context().forward(null, next.value);
                keyValueStore.delete(next.key);
            }
        }
    }

    @Override
    public void process(String key, Event value) {
        Event event = Event.builder(value).payload(value.getPayload().toUpperCase()).build();
        keyValueStore.put(event.getEventType().name() + " " + event.getId(), event);
    }

    public static String getName() {
        return "sort-processor";
    }
}

可执行代码为here。我在这里使用了一个简单的内存状态存储。如果您预计会突然发生大量事件，则可以使用其他答案中已经建议的持久状态存储。

Answer 2

KafkaStream允许您实现可查询状态存储。然后，您可以通过调用方法kafkaStream#store()获得对商店的只读访问权限。

如果您定义持久存储，KafkaStreams将使用RocksDB来存储您的数据。返回的KeyValueIterator实例将使用RocksDB迭代器，该迭代器将允许您以排序方式Rocks Iterator-Implementation遍历键值。

示例：

    KafkaStreams streams = new KafkaStreams(topology, props);
    ReadOnlyKeyValueStore<Object, Object> store = streams.store("storeName", QueryableStoreTypes.keyValueStore());
    KeyValueIterator<Object, Object> iterator = store.all();

如何从KTable获取排序的KeyValueStore？

2 个答案: