Spark streaming DStream RDD to get file name - scala

Question

Spark streaming textFileStream and fileStream can monitor a directory and process the new files in a Dstream RDD.
How to get the file names that are being processed by the DStream RDD at that particular interval?

Answer 1

fileStream produces UnionRDD of NewHadoopRDDs. The good part about NewHadoopRDDs created by sc.newAPIHadoopFile is that their names are set to their paths.
Here's the example of what you can do with that knowledge:
def namedTextFileStream(ssc: StreamingContext, directory: String): DStream[String] =
ssc.fileStream[LongWritable, Text, TextInputFormat](directory)
.transform( rdd =>
new UnionRDD(rdd.context,
rdd.dependencies.map( dep =>
dep.rdd.asInstanceOf[RDD[(LongWritable, Text)]].map(_._2.toString).setName(dep.rdd.name)
)
)
)
def transformByFile[U: ClassTag](unionrdd: RDD[String],
transformFunc: String => RDD[String] => RDD[U]): RDD[U] = {
new UnionRDD(unionrdd.context,
unionrdd.dependencies.map{ dep =>
if (dep.rdd.isEmpty) None
else {
val filename = dep.rdd.name
Some(
transformFunc(filename)(dep.rdd.asInstanceOf[RDD[String]])
.setName(filename)
)
}
}.flatten
)
}
def main(args: Array[String]) = {
val conf = new SparkConf()
.setAppName("Process by file")
.setMaster("local[2]")
val ssc = new StreamingContext(conf, Seconds(30))
val dstream = namesTextFileStream(ssc, "/some/directory")
def byFileTransformer(filename: String)(rdd: RDD[String]): RDD[(String, String)] =
rdd.map(line => (filename, line))
val transformed = dstream.
transform(rdd => transformByFile(rdd, byFileTransformer))
// Do some stuff with transformed
ssc.start()
ssc.awaitTermination()
}

Answer 2

For those that want some Java code instead of Scala:
JavaPairInputDStream<LongWritable, Text> textFileStream =
jsc.fileStream(
inputPath,
LongWritable.class,
Text.class,
TextInputFormat.class,
FileInputDStream::defaultFilter,
false
);
JavaDStream<Tuple2<String, String>> namedTextFileStream = textFileStream.transform((pairRdd, time) -> {
UnionRDD<Tuple2<LongWritable, Text>> rdd = (UnionRDD<Tuple2<LongWritable, Text>>) pairRdd.rdd();
List<RDD<Tuple2<LongWritable, Text>>> deps = JavaConverters.seqAsJavaListConverter(rdd.rdds()).asJava();
List<RDD<Tuple2<String, String>>> collectedRdds = deps.stream().map( depRdd -> {
if (depRdd.isEmpty()) {
return null;
}
JavaRDD<Tuple2<LongWritable, Text>> depJavaRdd = depRdd.toJavaRDD();
String filename = depRdd.name();
JavaPairRDD<String, String> newDep = JavaPairRDD.fromJavaRDD(depJavaRdd).mapToPair(t -> new Tuple2<String, String>(filename, t._2().toString())).setName(filename);
return newDep.rdd();
}).filter(t -> t != null).collect(Collectors.toList());
Seq<RDD<Tuple2<String, String>>> rddSeq = JavaConverters.asScalaBufferConverter(collectedRdds).asScala().toIndexedSeq();
ClassTag<Tuple2<String, String>> classTag = scala.reflect.ClassTag$.MODULE$.apply(Tuple2.class);
return new UnionRDD<Tuple2<String, String>>(rdd.sparkContext(), rddSeq, classTag).toJavaRDD();
});

Answer 3

Alternatively, by modifying FileInputDStream so that rather than loading the contents of the files into the RDD, it simply creates an RDD from the filenames.
This gives a performance boost if you don't actually want to read the data itself into the RDD, or want to pass filenames to an external command as one of your steps.
Simply change filesToRDD(..) so that it makes an RDD of the filenames, rather than loading the data into the RDD.
See: https://github.com/HASTE-project/bin-packing-paper/blob/master/spark/spark-scala-cellprofiler/src/main/scala/FileInputDStream2.scala#L278