如何使用 Flink 按事件时间对流进行排序 SQL

Question

我有一个乱序的 DataStream<Event> 我想对其进行排序，以便事件按事件时间戳排序。我已将我的用例简化为我的事件 class 只有一个字段——timestamp 字段：

public static void main(String[] args) throws Exception {
    StreamExecutionEnvironment env = StreamExecutionEnvironment.getExecutionEnvironment();
    StreamTableEnvironment tableEnv = TableEnvironment.getTableEnvironment(env);

    env.setStreamTimeCharacteristic(TimeCharacteristic.EventTime);
    env.setParallelism(1);

    DataStream<Event> eventStream = env.addSource(new OutOfOrderEventSource())
            .assignTimestampsAndWatermarks(new TimestampsAndWatermarks());

    Table events = tableEnv.fromDataStream(eventStream, "timestamp.rowtime");
    tableEnv.registerTable("events", events);
    Table sorted = tableEnv.sqlQuery("SELECT timestamp FROM events ORDER BY eventTime ASC");
    DataStream<Row> sortedEventStream = tableEnv.toAppendStream(sorted, Row.class);

    sortedEventStream.print();

    env.execute();
}

我收到这个错误：

Exception in thread "main" org.apache.flink.table.api.SqlParserException: SQL parse failed. Encountered "timestamp FROM" at line 1, column 8.

好像我没有以正确的方式指定事件时间属性，但不清楚哪里出了问题。

Answer 1

问题原来是在我的事件 class 中使用 timestamp 作为字段名称。将其更改为 eventTime 足以让一切正常工作：

public class Sort {
    public static final int OUT_OF_ORDERNESS = 1000;

    public static void main(String[] args) throws Exception {

        StreamExecutionEnvironment env = StreamExecutionEnvironment.getExecutionEnvironment();
        StreamTableEnvironment tableEnv = TableEnvironment.getTableEnvironment(env);

        env.setStreamTimeCharacteristic(TimeCharacteristic.EventTime);
        env.setParallelism(1);

        DataStream<Event> eventStream = env.addSource(new OutOfOrderEventSource())
                .assignTimestampsAndWatermarks(new TimestampsAndWatermarks());

        Table events = tableEnv.fromDataStream(eventStream, "eventTime.rowtime");
        tableEnv.registerTable("events", events);
        Table sorted = tableEnv.sqlQuery("SELECT eventTime FROM events ORDER BY eventTime ASC");
        DataStream<Row> sortedEventStream = tableEnv.toAppendStream(sorted, Row.class);

        sortedEventStream.print();

        env.execute();
    }

    public static class Event {
        public Long eventTime;

        Event() {
            this.eventTime = Instant.now().toEpochMilli() + (new Random().nextInt(OUT_OF_ORDERNESS));
        }
    }

    private static class OutOfOrderEventSource implements SourceFunction<Event> {
        private volatile boolean running = true;

        @Override
        public void run(SourceContext<Event> ctx) throws Exception {
            while(running) {
                ctx.collect(new Event());
                Thread.sleep(1);
            }
        }

        @Override
        public void cancel() {
            running = false;
        }
    }

    private static class TimestampsAndWatermarks extends BoundedOutOfOrdernessTimestampExtractor<Event> {
        public TimestampsAndWatermarks() {
            super(Time.milliseconds(OUT_OF_ORDERNESS));
        }

        @Override
        public long extractTimestamp(Event event) {
            return event.eventTime;
        }
    }
}

如何使用 Flink 按事件时间对流进行排序 SQL

How to sort a stream by event time using Flink SQL

apache-flink

flink-streaming

flink-sql