如何为具有状态的自定义触发器实现保存点？

Question

我已经实现了自定义WindowAssigher：

public class SessionWindowAssigner extends WindowAssigner<LogItem, SessionWindow> {
    @Override
    public Collection<SessionWindow> assignWindows(LogItem element, long timestamp) {
        return Collections.singletonList(new SessionWindow(element.getSessionUid()));
    }

    @Override
    public Trigger<LogItem, SessionWindow> getDefaultTrigger(StreamExecutionEnvironment env) {
        return new SessionTrigger(60_000L);
    }

    @Override
    public TypeSerializer<SessionWindow> getWindowSerializer(ExecutionConfig executionConfig) {
        return new SessionWindow.Serializer();
    }
}

，Window：

public class SessionWindow extends Window {
    private final String sessionUid;

    public SessionWindow(String sessionUid) {
        this.sessionUid = sessionUid;
    }

    public String getSessionUid() {
        return sessionUid;
    }

    @Override
    public long maxTimestamp() {
        return Long.MAX_VALUE;
    }

    @Override
    public boolean equals(Object o) {
        if (this == o) return true;
        if (o == null || getClass() != o.getClass()) return false;

        SessionWindow that = (SessionWindow) o;

        return sessionUid.equals(that.sessionUid);
    }

    @Override
    public int hashCode() {
        return sessionUid.hashCode();
    }

    public static class Serializer extends TypeSerializer<SessionWindow> {
        private static final long serialVersionUID = 1L;

        @Override
        public boolean isImmutableType() {
            return true;
        }

        @Override
        public TypeSerializer<SessionWindow> duplicate() {
            return this;
        }

        @Override
        public SessionWindow createInstance() {
            return null;
        }

        @Override
        public SessionWindow copy(SessionWindow from) {
            return from;
        }

        @Override
        public SessionWindow copy(SessionWindow from, SessionWindow reuse) {
            return from;
        }

        @Override
        public int getLength() {
            return 0;
        }

        @Override
        public void serialize(SessionWindow record, DataOutputView target) throws IOException {
            target.writeUTF(record.sessionUid);
        }

        @Override
        public SessionWindow deserialize(DataInputView source) throws IOException {
            return new SessionWindow(source.readUTF());
        }

        @Override
        public SessionWindow deserialize(SessionWindow reuse, DataInputView source) throws IOException {
            return new SessionWindow(source.readUTF());
        }

        @Override
        public void copy(DataInputView source, DataOutputView target) throws IOException {
            target.writeUTF(source.readUTF());
        }

        @Override
        public boolean equals(Object obj) {
            return obj instanceof Serializer;
        }

        @Override
        public boolean canEqual(Object obj) {
            return obj instanceof Serializer;
        }

        @Override
        public int hashCode() {
            return 0;
        }
    }
}

和Trigger：

public class SessionTrigger extends Trigger<LogItem, SessionWindow> {
    private final long sessionTimeout;

    private final ValueStateDescriptor<Long> previousFinishTimestampDesc = new ValueStateDescriptor<>("SessionTrigger.timestamp", LongSerializer.INSTANCE, null);

    public SessionTrigger(long sessionTimeout) {
        this.sessionTimeout = sessionTimeout;
    }

    @Override
    public TriggerResult onElement(LogItem element, long timestamp, SessionWindow window, TriggerContext ctx) throws Exception {
        ValueState<Long> previousFinishTimestampState = ctx.getPartitionedState(previousFinishTimestampDesc);

        Long previousFinishTimestamp = previousFinishTimestampState.value();
        Long newFinisTimestamp = timestamp + sessionTimeout;

        if (previousFinishTimestamp != null) {
            ctx.deleteEventTimeTimer(previousFinishTimestamp);
        }

        ctx.registerEventTimeTimer(newFinisTimestamp);

        previousFinishTimestampState.update(newFinisTimestamp);

        return TriggerResult.CONTINUE;
    }

    @Override
    public TriggerResult onEventTime(long time, SessionWindow window, TriggerContext ctx) throws Exception {
        return TriggerResult.FIRE_AND_PURGE;
    }

    @Override
    public TriggerResult onProcessingTime(long time, SessionWindow window, TriggerContext ctx) throws Exception {
        throw new UnsupportedOperationException("This is not processing time trigger");
    }

    @Override
    public void clear(SessionWindow window, TriggerContext ctx) throws Exception {
        ValueState<Long> previousFinishTimestampState = ctx.getPartitionedState(previousFinishTimestampDesc);

        Long previousFinishTimestamp = previousFinishTimestampState.value();

        ctx.deleteEventTimeTimer(previousFinishTimestamp);

        previousFinishTimestampState.clear();
    }
}

通过超时检测会话结束，即如果最后一个事件是 N 秒前，则评估窗口函数。如您所见，我正在 ValueState 中保存最后一个事件时间戳，因为我想在失败后恢复它。

似乎我应该在此触发器中为保存/恢复保存点（和检查点）快照实现 Checkpointed 接口，因为我不想在重新部署流程期间丢失触发器状态。

那么，谁能解释我如何在部署期间正确保存SessionTrigger 触发器（以及可能相关的窗口）的状态？

据我了解，我应该为SessionTrigger 实现Checkpointed 接口，因为只有它有状态。对？ SessionWindow-s 和 SessionWindowAssigner 怎么样？部署后会自动恢复还是我应该手动恢复？

Answer 1

取自SessionWindowing

private static class SessionTrigger extends Trigger<Tuple3<String, Long, Integer>, GlobalWindow> {

    private static final long serialVersionUID = 1L;

    private final Long sessionTimeout;

    private final ValueStateDescriptor<Long> stateDesc = 
            new ValueStateDescriptor<>("last-seen", Long.class, -1L);


    public SessionTrigger(Long sessionTimeout) {
        this.sessionTimeout = sessionTimeout;

    }

    @Override
    public TriggerResult onElement(Tuple3<String, Long, Integer> element, long timestamp, GlobalWindow window, TriggerContext ctx) throws Exception {

        ValueState<Long> lastSeenState = ctx.getPartitionedState(stateDesc);
        Long lastSeen = lastSeenState.value();

        Long timeSinceLastEvent = timestamp - lastSeen;

        ctx.deleteEventTimeTimer(lastSeen + sessionTimeout);

        // Update the last seen event time
        lastSeenState.update(timestamp);

        ctx.registerEventTimeTimer(timestamp + sessionTimeout);

        if (lastSeen != -1 && timeSinceLastEvent > sessionTimeout) {
            System.out.println("FIRING ON ELEMENT: " + element + " ts: " + timestamp + " last " + lastSeen);
            return TriggerResult.FIRE_AND_PURGE;
        } else {
            return TriggerResult.CONTINUE;
        }
    }

    @Override
    public TriggerResult onEventTime(long time, GlobalWindow window, TriggerContext ctx) throws Exception {
        ValueState<Long> lastSeenState = ctx.getPartitionedState(stateDesc);
        Long lastSeen = lastSeenState.value();

        if (time - lastSeen >= sessionTimeout) {
            System.out.println("CTX: " + ctx + " Firing Time " + time + " last seen " + lastSeen);
            return TriggerResult.FIRE_AND_PURGE;
        }
        return TriggerResult.CONTINUE;
    }

    @Override
    public TriggerResult onProcessingTime(long time, GlobalWindow window, TriggerContext ctx) throws Exception {
        return TriggerResult.CONTINUE;
    }

    @Override
    public void clear(GlobalWindow window, TriggerContext ctx) throws Exception {
        ValueState<Long> lastSeenState = ctx.getPartitionedState(stateDesc);
        if (lastSeenState.value() != -1) {
            ctx.deleteEventTimeTimer(lastSeenState.value() + sessionTimeout);
        }
        lastSeenState.clear();
    }
}