Write and read raw byte arrays in Spark - using Sequence File SequenceFile

scala hadoop hdfs apache-spark sequencefile
samthebest picture samthebest · Jun 6, 2014 · Viewed 11.4k times · Source

How do you write RDD[Array[Byte]] to a file using Apache Spark and read it back again?

Answer

samthebest picture samthebest · Jun 6, 2014

Common problems seem to be getting a weird cannot cast exception from BytesWritable to NullWritable. Other common problem is BytesWritable getBytes is a totally pointless pile of nonsense which doesn't get bytes at all. What getBytes does is get your bytes than adds a ton of zeros on the end! You have to use copyBytes

val rdd: RDD[Array[Byte]] = ???

// To write
rdd.map(bytesArray => (NullWritable.get(), new BytesWritable(bytesArray)))
  .saveAsSequenceFile("/output/path", codecOpt)

// To read
val rdd: RDD[Array[Byte]] = sc.sequenceFile[NullWritable, BytesWritable]("/input/path")
  .map(_._2.copyBytes())

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