Tejas Patil created SPARK-18035:
-----------------------------------

             Summary: Unwrapping java maps in HiveInspectors allocates 
unnecessary buffer
                 Key: SPARK-18035
                 URL: https://issues.apache.org/jira/browse/SPARK-18035
             Project: Spark
          Issue Type: Bug
          Components: SQL
    Affects Versions: 2.0.1
            Reporter: Tejas Patil
            Priority: Minor


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)
```



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