问题
I am trying to compute the temperature average of 3 different rooms where each room has 3 temperature sensors. I am using Flink (in Java). First I split the sensors by a key that is the room (A, B, or C) and them I create a RichFlatMapFunction which holds a MapState to save the temperature while I don't have until 3 measurements. After three measurements I compute the average. In order to use the MapState I need a MapStateDescriptor which I don't know how to instantiate properly. Can someone help me with this? Thanks.
public class SensorsMultipleReadingMqttEdgentQEP2 {
private boolean checkpointEnable = false;
private long checkpointInterval = 10000;
private CheckpointingMode checkpointMode = CheckpointingMode.EXACTLY_ONCE;
public SensorsMultipleReadingMqttEdgentQEP2() throws Exception {
StreamExecutionEnvironment env = StreamExecutionEnvironment.getExecutionEnvironment();
env.setStreamTimeCharacteristic(TimeCharacteristic.IngestionTime);
if (checkpointEnable) {
env.enableCheckpointing(checkpointInterval, checkpointMode);
}
DataStream<MqttTemperature> temperatureStream01 = env.addSource(new TemperatureMqttConsumer("topic-edgent-01"));
DataStream<MqttTemperature> temperatureStream02 = env.addSource(new TemperatureMqttConsumer("topic-edgent-02"));
DataStream<MqttTemperature> temperatureStream03 = env.addSource(new TemperatureMqttConsumer("topic-edgent-03"));
DataStream<Tuple2<String, Double>> averageStream01 = temperatureStream01.map(new SensorMatcher()).keyBy(0)
.flatMap(new AverageTempMapper());
DataStream<Tuple2<String, Double>> averageStream02 = temperatureStream02.map(new SensorMatcher()).keyBy(0)
.flatMap(new AverageTempMapper());
DataStream<Tuple2<String, Double>> averageStream03 = temperatureStream03.map(new SensorMatcher()).keyBy(0)
.flatMap(new AverageTempMapper());
DataStream<Tuple2<String, Double>> averageStreams = averageStream01.union(averageStream02)
.union(averageStream03);
averageStreams.print();
env.execute("SensorsMultipleReadingMqttEdgentQEP");
}
public static class SensorMatcher implements MapFunction<MqttTemperature, Tuple2<String, MqttTemperature>> {
private static final long serialVersionUID = 7035756567190539683L;
@Override
public Tuple2<String, MqttTemperature> map(MqttTemperature value) throws Exception {
String key = "no-room";
if (value.getId().equals(1) || value.getId().equals(2) || value.getId().equals(3)) {
key = "room-A";
} else if (value.getId().equals(4) || value.getId().equals(5) || value.getId().equals(6)) {
key = "room-B";
} else if (value.getId().equals(7) || value.getId().equals(8) || value.getId().equals(9)) {
key = "room-C";
} else {
System.err.println("Sensor not defined in any room.");
}
return new Tuple2<>(key, value);
}
}
public static class AverageTempMapper
extends RichFlatMapFunction<Tuple2<String, MqttTemperature>, Tuple2<String, Double>> {
private static final long serialVersionUID = -4780146677198295204L;
private MapState<String, Tuple2<Integer, Double>> modelState;
@Override
public void open(Configuration parameters) throws Exception {
TypeInformation<Tuple2<String, Tuple2<Integer, Double>>> typeInformation = TypeInformation
.of(new TypeHint<Tuple2<String, Tuple2<Integer, Double>>>() {
});
// HOW TO INSTANTIATE THIS descriptor?
MapStateDescriptor<String, Tuple2<Integer, Double>> descriptor = new MapStateDescriptor<>("modelState",
String.class, Tuple2.class);
modelState = getRuntimeContext().getMapState(descriptor);
}
@Override
public void flatMap(Tuple2<String, MqttTemperature> value, Collector<Tuple2<String, Double>> out)
throws Exception {
Double temp = null;
Integer count = 0;
if (modelState.contains(value.f0)) {
count = modelState.get(value.f0).f0 + 1;
temp = (modelState.get(value.f0).f1 + value.f1.getTemp());
} else {
count = 1;
temp = value.f1.getTemp();
}
modelState.put(value.f0, Tuple2.of(count, temp));
if (count >= 3) {
out.collect(Tuple2.of("room", null));
}
}
}
}
回答1:
In order to define the MapStateDescriptor you could do the following:
MapStateDescriptor<String, Tuple2<Integer, Double>> modelState = new MapStateDescriptor<>(
"modelState",
BasicTypeInfo.STRING_TYPE_INFO,
TupleTypeInfo.getBasicTupleTypeInfo(Integer.class, Double.class));
this.modelState = getRuntimeContext().getMapState(modelState);
However, there is actually no need to use a MapState in your case. Since the stream is already keyed it is enough to use a ValueState. The code would look the following way:
public static class AverageTempMapper extends RichFlatMapFunction<Tuple2<String, MqttTemperature>, Tuple2<String, Double>> {
private static final long serialVersionUID = -4780146677198295204L;
private ValueState<Tuple2<Integer, Double>> modelState;
@Override
public void open(Configuration parameters) {
this.modelState = getRuntimeContext().getState(new ValueStateDescriptor<>("modelState", TupleTypeInfo.getBasicTupleTypeInfo(Integer.class, Double.class)));
}
@Override
public void flatMap(Tuple2<String, MqttTemperature> value, Collector<Tuple2<String, Double>> out) throws Exception {
Double temp;
Integer count;
if (modelState.value() != null) {
Tuple2<Integer, Double> state = modelState.value();
count = state.f0 + 1;
temp = state.f1 + value.f1.getTemp();
} else {
count = 1;
temp = value.f1.getTemp();
}
modelState.update(Tuple2.of(count, temp));
if (count >= 3) {
out.collect(Tuple2.of(value.f0, temp/count));
}
}
}
回答2:
I did in some way that I think is reasonable. At least it is working. If someone has a better approach to compute multiple averages could you comment, please?
public class SensorsMultipleReadingMqttEdgentQEP2 {
private boolean checkpointEnable = false;
private long checkpointInterval = 10000;
private CheckpointingMode checkpointMode = CheckpointingMode.EXACTLY_ONCE;
public SensorsMultipleReadingMqttEdgentQEP2() throws Exception {
// Start streaming from fake data source sensors
StreamExecutionEnvironment env = StreamExecutionEnvironment.getExecutionEnvironment();
// obtain execution environment, run this example in "ingestion time"
env.setStreamTimeCharacteristic(TimeCharacteristic.IngestionTime);
if (checkpointEnable) {
env.enableCheckpointing(checkpointInterval, checkpointMode);
}
DataStream<MqttTemperature> temperatureStream01 = env.addSource(new TemperatureMqttConsumer("topic-edgent-01"));
DataStream<MqttTemperature> temperatureStream02 = env.addSource(new TemperatureMqttConsumer("topic-edgent-02"));
DataStream<MqttTemperature> temperatureStream03 = env.addSource(new TemperatureMqttConsumer("topic-edgent-03"));
DataStream<Tuple2<String, Double>> averageStream01 = temperatureStream01.map(new SensorMatcher()).keyBy(0)
.flatMap(new AverageTempMapper());
DataStream<Tuple2<String, Double>> averageStream02 = temperatureStream02.map(new SensorMatcher()).keyBy(0)
.flatMap(new AverageTempMapper());
DataStream<Tuple2<String, Double>> averageStream03 = temperatureStream03.map(new SensorMatcher()).keyBy(0)
.flatMap(new AverageTempMapper());
DataStream<Tuple2<String, Double>> averageStreams = averageStream01.union(averageStream02)
.union(averageStream03);
averageStreams.print();
env.execute("SensorsMultipleReadingMqttEdgentQEP");
}
public static class SensorMatcher implements MapFunction<MqttTemperature, Tuple2<String, MqttTemperature>> {
private static final long serialVersionUID = 7035756567190539683L;
@Override
public Tuple2<String, MqttTemperature> map(MqttTemperature value) throws Exception {
String key = "no-room";
if (value.getId().equals(1) || value.getId().equals(2) || value.getId().equals(3)) {
key = "room-A";
} else if (value.getId().equals(4) || value.getId().equals(5) || value.getId().equals(6)) {
key = "room-B";
} else if (value.getId().equals(7) || value.getId().equals(8) || value.getId().equals(9)) {
key = "room-C";
} else {
System.err.println("Sensor not defined in any room.");
}
return new Tuple2<>(key, value);
}
}
public static class AverageTempMapper
extends RichFlatMapFunction<Tuple2<String, MqttTemperature>, Tuple2<String, Double>> {
private static final long serialVersionUID = -4780146677198295204L;
private MapState<String, Tuple2<Integer, Double>> modelState;
private Integer threshold = 3;
@Override
public void open(Configuration parameters) throws Exception {
TypeInformation<Tuple2<Integer, Double>> typeInformation = TypeInformation
.of(new TypeHint<Tuple2<Integer, Double>>() {
});
MapStateDescriptor<String, Tuple2<Integer, Double>> descriptor = new MapStateDescriptor<String, Tuple2<Integer, Double>>(
"modelState", TypeInformation.of(String.class), typeInformation);
modelState = getRuntimeContext().getMapState(descriptor);
}
@Override
public void flatMap(Tuple2<String, MqttTemperature> value, Collector<Tuple2<String, Double>> out)
throws Exception {
Integer count = 0;
Double temp = 0.0;
if (modelState.contains(value.f0)) {
// there is already a value on the state
count = modelState.get(value.f0).f0 + 1;
temp = modelState.get(value.f0).f1 + value.f1.getTemp();
modelState.put(value.f0, Tuple2.of(1, value.f1.getTemp()));
} else {
// there is no value on the state
count = 1;
temp = value.f1.getTemp();
}
modelState.put(value.f0, Tuple2.of(count, temp));
if (count >= threshold) {
// only compute the average after the threshold
out.collect(Tuple2.of(value.f0, temp / count));
// clear the modelState value in order to compute new values next time
modelState.put(value.f0, Tuple2.of(0, 0.0));
}
}
}
}
来源：https://stackoverflow.com/questions/54535419/how-to-instantiate-a-mapstatedescriptor-in-fink-to-compute-multiple-averages-str