Minor Description
In HiveInspectors, I saw that converting Java map to Spark's `ArrayBasedMapData` spent quite sometime in buffer copying : https://github.com/apache/spark/blob/master/sql/hive/src/main/scala/org/apache/spark/sql/hive/HiveInspectors.scala#L658
The reason being `map.toSeq` allocates a new buffer and copies the map entries to it: https://github.com/scala/scala/blob/2.11.x/src/library/scala/collection/MapLike.scala#L323
This copy is not needed as we get rid of it once we extract the key and value arrays.
Here is the call trace:
org.apache.spark.sql.hive.HiveInspectors$$anonfun$unwrapperFor$41.apply(HiveInspectors.scala:664) scala.collection.AbstractMap.toSeq(Map.scala:59) scala.collection.MapLike$class.toSeq(MapLike.scala:323) scala.collection.AbstractMap.toBuffer(Map.scala:59) scala.collection.MapLike$class.toBuffer(MapLike.scala:326) scala.collection.AbstractTraversable.copyToBuffer(Traversable.scala:104) scala.collection.TraversableOnce$class.copyToBuffer(TraversableOnce.scala:275) scala.collection.mutable.ArrayBuffer.$plus$plus$eq(ArrayBuffer.scala:48) scala.collection.mutable.ArrayBuffer.$plus$plus$eq(ArrayBuffer.scala:104) scala.collection.generic.Growable$class.$plus$plus$eq(Growable.scala:59) scala.collection.AbstractIterable.foreach(Iterable.scala:54) scala.collection.IterableLike$class.foreach(IterableLike.scala:72) scala.collection.AbstractIterator.foreach(Iterator.scala:1336) scala.collection.Iterator$class.foreach(Iterator.scala:893) scala.collection.generic.Growable$$anonfun$$plus$plus$eq$1.apply(Growable.scala:59) scala.collection.generic.Growable$$anonfun$$plus$plus$eq$1.apply(Growable.scala:59)
