It is definitely a solution ;)

You should be aware of the downsides though:



On 21/02/2019 14:18, Stephen Connolly wrote:
Yes, it was the "watermarks for event time when no events for that shard" problem.

I am now investigating whether we can use a blended watermark of max(lastEventTimestamp - 1min, System.currentTimeMillis() - 5min) to ensure idle shards do not cause excessive data retention.

Is that the best solution?

On Thu, 21 Feb 2019 at 08:30, Dawid Wysakowicz <> wrote:

Hi Stephen,

Watermark for a single operator is the minimum of Watermarks received from all inputs, therefore if one of your shards/operators does not have incoming data it will not produce Watermarks thus the Watermark of WindowOperator will not progress. So this is sort of an expected behavior.

I recommend reading the docs linked by Congxian, especially this section[1].




On 19/02/2019 14:31, Stephen Connolly wrote:
Hmmm my suspicions are now quite high. I created a file source that just replays the events straight then I get more results....

On Tue, 19 Feb 2019 at 11:50, Stephen Connolly <> wrote:
Hmmm after expanding the dataset such that there was additional data that ended up on shard-0 (everything in my original dataset was coincidentally landing on shard-1) I am now getting output... should I expect this kind of behaviour if no data arrives at shard-0 ever?

On Tue, 19 Feb 2019 at 11:14, Stephen Connolly <> wrote:
Hi, I’m having a strange situation and I would like to know where I should start trying to debug.

I have set up a configurable swap in source, with three implementations:

1. A mock implementation
2. A Kafka consumer implementation
3. A Kinesis consumer implementation

From injecting a log and no-op map function I can see that all three sources pass through the events correctly.

I then have a window based on event time stamps… and from inspecting the aggregation function I can see that the data is getting aggregated…, I’m using the `.aggregate(AggregateFunction.WindowFunction)` variant so that I can retrieve the key

Here’s the strange thing, I only change the source (and each source uses the same deserialization function) but:

  • When I use either Kafka or my Mock source, the WindowFunction gets called as events pass the end of the window
  • When I use the Kinesis source, however, the window function never gets called. I have even tried injecting events into kinesis with really high timestamps to flush the watermarks in my BoundedOutOfOrdernessTimestampExtractor... but nothing
I cannot see how this source switching could result in such a different behaviour:

        Properties sourceProperties = new Properties();
        ConsumerFactory sourceFactory;
        String sourceName = configParams.getRequired("source");
        switch (sourceName.toLowerCase(Locale.ENGLISH)) {
            case "kinesis":
                sourceFactory = FlinkKinesisConsumer::new;
                copyOptionalArg(configParams, "aws-region", sourceProperties, AWSConfigConstants.AWS_REGION);
                copyOptionalArg(configParams, "aws-endpoint", sourceProperties, AWSConfigConstants.AWS_ENDPOINT);
                copyOptionalArg(configParams, "aws-access-key", sourceProperties, AWSConfigConstants.AWS_ACCESS_KEY_ID);
                copyOptionalArg(configParams, "aws-secret-key", sourceProperties, AWSConfigConstants.AWS_SECRET_ACCESS_KEY);
                copyOptionalArg(configParams, "aws-profile", sourceProperties, AWSConfigConstants.AWS_PROFILE_NAME);
            case "kafka":
                sourceFactory = FlinkKafkaConsumer010::new;
                copyRequiredArg(configParams, "bootstrap-server", sourceProperties, "bootstrap.servers");
                copyOptionalArg(configParams, "group-id", sourceProperties, "");
            case "mock":
                sourceFactory = MockSourceFunction::new;
                throw new RuntimeException("Unknown source '" + sourceName + '\'');

        // set up the streaming execution environment
        final StreamExecutionEnvironment env = StreamExecutionEnvironment.getExecutionEnvironment();

        // poll watermark every second because using BoundedOutOfOrdernessTimestampExtractor

        SplitStream<JsonNode> eventsByType = env.addSource(sourceFactory.create(
                new ObjectNodeDeserializationSchema(),
                .returns(ObjectNode.class) // the use of ConsumerFactory erases the type info so add it back
                        new ObjectNodeBoundedOutOfOrdernessTimestampExtractor("timestamp", Time.seconds(5))
                .split(new JsonNodeOutputSelector("eventType"));
                .keyBy(new JsonNodeStringKeySelector("_key"))
                        (KeySelector<JsonNode, Time>) TasksMain::offsetPerMaster))
                .aggregate(new CountsAggregator<>(), new KeyTagger<>()) // <==== The CountsAggregator is seeing the data
                .print() // <==== HERE is where we get no output from Kinesis... but Kafka and my Mock are just fine!