I am reading Hadoop Sequence Files using Spark(v1.6.1). After caching the RDD, the contents in RDD becomes invalid(the last entry duplicated n
times).
Here is my code snippet:
import org.apache.hadoop.io.Text
import org.apache.hadoop.mapred.SequenceFileOutputFormat
import org.apache.spark.{SparkConf, SparkContext}
object Main {
def main(args: Array[String]) {
val seqfile = "data-1.seq"
val conf: SparkConf = new SparkConf()
.setAppName("..Buffer..")
.setMaster("local")
.registerKryoClasses(Array(classOf[Text]))
val sc = new SparkContext(conf)
sc.parallelize((0 to 1000).toSeq) //creating a sample sequence file
.map(i => (new Text(s"$i"), new Text(s"${i*i}")))
.saveAsHadoopFile(seqfile, classOf[Text], classOf[Text],
classOf[SequenceFileOutputFormat[Text, Text]])
val c = sc.sequenceFile(seqfile, classOf[Text], classOf[Text])
.cache()
.map(t => {println(t); t})
.collectAsMap()
println(c)
println(c.size)
sc.stop()
}
}
The output:
(1000,1000000)
(1000,1000000)
(1000,1000000)
(1000,1000000)
(1000,1000000)
...... //Total 1000 lines with same content as above ...
Map(1000 -> 1000000)
1
EDIT :
For future visitors : If you are reading sequence file like I did in the above code snippet, refer to accepted answer. A simple workaround is to make a copy of Hadoop Writable
instance:
val c = sc.sequenceFile(seqfile, classOf[Text], classOf[Text])
.map(t =>(new Text(t._1), new Text(t._2))) //Make copy of writable instances
Please refer to the comments in sequenceFile.
/** Get an RDD for a Hadoop SequenceFile with given key and value types.
*
* '''Note:''' Because Hadoop's RecordReader class re-uses the same Writable object for each
* record, directly caching the returned RDD or directly passing it to an aggregation or shuffle
* operation will create many references to the same object.
* If you plan to directly cache, sort, or aggregate Hadoop writable objects, you should first
* copy them using a `map` function.
*/