[SparkSQL ] What is Exchange in physical plan for ?

Hi, DataFrame.explain() shows the physical plan of a query. I noticed there are a lot of `Exchange`s in it, like below: Project [period#20L,categoryName#0,regionName#10,action#15,list_id#16L] ShuffledHashJoin [region#18], [regionCode#9], BuildRight Exchange (HashPartitioning [region#18], 12)

scala.MatchError on SparkSQL when creating ArrayType of StructType

Hi, I am using SparkSQL on 1.1.0 branch. The following code leads to a scala.MatchError at org.apache.spark.sql.catalyst.expressions.Cast.cast$lzycompute(Cast.scala:247) val scm = StructType(*inputRDD*.schema.fields.init :+ StructField(list, ArrayType( StructType(