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序
本文主要研究一下 flink DataStream 的 split 操作
实例
SplitStream<Integer> split = someDataStream.split(new OutputSelector<Integer>() {
@Override
public Iterable<String> select(Integer value) {
List<String> output = new ArrayList<String>();
if (value % 2 == 0) {
output.add(“even”);
}
else {
output.add(“odd”);
}
return output;
}
});
本实例将 dataStream split 为两个 dataStream，一个 outputName 为 even，另一个 outputName 为 odd
DataStream.split
flink-streaming-java_2.11-1.7.0-sources.jar!/org/apache/flink/streaming/api/datastream/DataStream.java
@Public
public class DataStream<T> {
//……
public SplitStream<T> split(OutputSelector<T> outputSelector) {
return new SplitStream<>(this, clean(outputSelector));
}
//……
}
DataStream 的 split 操作接收 OutputSelector 参数，然后创建并返回 SplitStream
OutputSelector
flink-streaming-java_2.11-1.7.0-sources.jar!/org/apache/flink/streaming/api/collector/selector/OutputSelector.java
@PublicEvolving
public interface OutputSelector<OUT> extends Serializable {
Iterable<String> select(OUT value);
}
OutputSelector 定义了 select 方法用于给 element 打上 outputNames
SplitStream
flink-streaming-java_2.11-1.7.0-sources.jar!/org/apache/flink/streaming/api/datastream/SplitStream.java
@PublicEvolving
public class SplitStream<OUT> extends DataStream<OUT> {
protected SplitStream(DataStream<OUT> dataStream, OutputSelector<OUT> outputSelector) {
super(dataStream.getExecutionEnvironment(), new SplitTransformation<OUT>(dataStream.getTransformation(), outputSelector));
}
public DataStream<OUT> select(String… outputNames) {
return selectOutput(outputNames);
}
private DataStream<OUT> selectOutput(String[] outputNames) {
for (String outName : outputNames) {
if (outName == null) {
throw new RuntimeException(“Selected names must not be null”);
}
}
SelectTransformation<OUT> selectTransform = new SelectTransformation<OUT>(this.getTransformation(), Lists.newArrayList(outputNames));
return new DataStream<OUT>(this.getExecutionEnvironment(), selectTransform);
}
}
SplitStream 继承了 DataStream，它定义了 select 方法，可以用来根据 outputNames 选择 split 出来的 dataStream；select 方法创建了 SelectTransformation
StreamGraphGenerator
flink-streaming-java_2.11-1.7.0-sources.jar!/org/apache/flink/streaming/api/graph/StreamGraphGenerator.java
@Internal
public class StreamGraphGenerator {
//……
private Collection<Integer> transform(StreamTransformation<?> transform) {
if (alreadyTransformed.containsKey(transform)) {
return alreadyTransformed.get(transform);
}
LOG.debug(“Transforming ” + transform);
if (transform.getMaxParallelism() <= 0) {
// if the max parallelism hasn’t been set, then first use the job wide max parallelism
// from theExecutionConfig.
int globalMaxParallelismFromConfig = env.getConfig().getMaxParallelism();
if (globalMaxParallelismFromConfig > 0) {
transform.setMaxParallelism(globalMaxParallelismFromConfig);
}
}
// call at least once to trigger exceptions about MissingTypeInfo
transform.getOutputType();
Collection<Integer> transformedIds;
if (transform instanceof OneInputTransformation<?, ?>) {
transformedIds = transformOneInputTransform((OneInputTransformation<?, ?>) transform);
} else if (transform instanceof TwoInputTransformation<?, ?, ?>) {
transformedIds = transformTwoInputTransform((TwoInputTransformation<?, ?, ?>) transform);
} else if (transform instanceof SourceTransformation<?>) {
transformedIds = transformSource((SourceTransformation<?>) transform);
} else if (transform instanceof SinkTransformation<?>) {
transformedIds = transformSink((SinkTransformation<?>) transform);
} else if (transform instanceof UnionTransformation<?>) {
transformedIds = transformUnion((UnionTransformation<?>) transform);
} else if (transform instanceof SplitTransformation<?>) {
transformedIds = transformSplit((SplitTransformation<?>) transform);
} else if (transform instanceof SelectTransformation<?>) {
transformedIds = transformSelect((SelectTransformation<?>) transform);
} else if (transform instanceof FeedbackTransformation<?>) {
transformedIds = transformFeedback((FeedbackTransformation<?>) transform);
} else if (transform instanceof CoFeedbackTransformation<?>) {
transformedIds = transformCoFeedback((CoFeedbackTransformation<?>) transform);
} else if (transform instanceof PartitionTransformation<?>) {
transformedIds = transformPartition((PartitionTransformation<?>) transform);
} else if (transform instanceof SideOutputTransformation<?>) {
transformedIds = transformSideOutput((SideOutputTransformation<?>) transform);
} else {
throw new IllegalStateException(“Unknown transformation: ” + transform);
}
// need this check because the iterate transformation adds itself before
// transforming the feedback edges
if (!alreadyTransformed.containsKey(transform)) {
alreadyTransformed.put(transform, transformedIds);
}
if (transform.getBufferTimeout() >= 0) {
streamGraph.setBufferTimeout(transform.getId(), transform.getBufferTimeout());
}
if (transform.getUid() != null) {
streamGraph.setTransformationUID(transform.getId(), transform.getUid());
}
if (transform.getUserProvidedNodeHash() != null) {
streamGraph.setTransformationUserHash(transform.getId(), transform.getUserProvidedNodeHash());
}
if (transform.getMinResources() != null && transform.getPreferredResources() != null) {
streamGraph.setResources(transform.getId(), transform.getMinResources(), transform.getPreferredResources());
}
return transformedIds;
}
private <T> Collection<Integer> transformSelect(SelectTransformation<T> select) {
StreamTransformation<T> input = select.getInput();
Collection<Integer> resultIds = transform(input);
// the recursive transform might have already transformed this
if (alreadyTransformed.containsKey(select)) {
return alreadyTransformed.get(select);
}
List<Integer> virtualResultIds = new ArrayList<>();
for (int inputId : resultIds) {
int virtualId = StreamTransformation.getNewNodeId();
streamGraph.addVirtualSelectNode(inputId, virtualId, select.getSelectedNames());
virtualResultIds.add(virtualId);
}
return virtualResultIds;
}
private <T> Collection<Integer> transformSplit(SplitTransformation<T> split) {
StreamTransformation<T> input = split.getInput();
Collection<Integer> resultIds = transform(input);
// the recursive transform call might have transformed this already
if (alreadyTransformed.containsKey(split)) {
return alreadyTransformed.get(split);
}
for (int inputId : resultIds) {
streamGraph.addOutputSelector(inputId, split.getOutputSelector());
}
return resultIds;
}
//……
}
StreamGraphGenerator 里头的 transform 会对 SelectTransformation 以及 SplitTransformation 进行相应的处理
transformSelect 方法会根据 select.getSelectedNames() 来 addVirtualSelectNode
transformSplit 方法则根据 split.getOutputSelector() 来 addOutputSelector
小结
DataStream 的 split 操作接收 OutputSelector 参数，然后创建并返回 SplitStream
OutputSelector 定义了 select 方法用于给 element 打上 outputNames
SplitStream 继承了 DataStream，它定义了 select 方法，可以用来根据 outputNames 选择 split 出来的 dataStream
doc
DataStream Transformations
