如何从 KTable 中获取排序后的 KeyValueStore？

Question

我想从 KStream 中具体化一个 KTable，我希望 KeyValueStore 按 Key 排序。

我尝试查找建议通过处理器 API 实现排序的 KTable API 规范 (https://kafka.apache.org/20/javadoc/org/apache/kafka/streams/kstream/KTable.html), but no 'sort'-method exists. I also looked up this article (https://dzone.com/articles/how-to-order-streamed-dataframes)。但是，我正在检查是否可以通过其他方式实现这一点？

Answer 1

KafkaStream 允许您物化可查询状态存储。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

如果您定义持久化存储，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，它允许您以排序方式迭代键值 Rocks Iterator-Implementation.

示例：

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

Answer 2

使用密钥将事件添加到 StateStore。 StateStore 返回的 KeyValueIterator 以有序的方式导航 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 : 
    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";
    }
}

可执行代码是here。我在这里使用了一个简单的内存状态存储。如果您预计会在短时间内发生大量事件，您可以使用其他答案中已经建议的持久状态存储。

如何从 KTable 中获取排序后的 KeyValueStore？

How to get a sorted KeyValueStore from a KTable?

apache-kafka

rocksdb

apache-kafka-streams