[SPARK-2631][SQL] Use SQLConf to configure in-memory columnar caching

Author: Michael Armbrust <michael@databricks.com>

Closes #1638 from marmbrus/cachedConfig and squashes the following commits:

2362082 [Michael Armbrust] Use SQLConf to configure in-memory columnar caching

sql/core/src/main/scala/org/apache/spark/sql/SQLConf.scala

@@ -22,6 +22,7 @@ import java.util.Properties
 import scala.collection.JavaConverters._
 
 object SQLConf {
+  val COMPRESS_CACHED = "spark.sql.inMemoryColumnarStorage.compressed"
   val AUTO_BROADCASTJOIN_THRESHOLD = "spark.sql.autoBroadcastJoinThreshold"
   val SHUFFLE_PARTITIONS = "spark.sql.shuffle.partitions"
   val DEFAULT_SIZE_IN_BYTES = "spark.sql.defaultSizeInBytes"
@@ -49,6 +50,9 @@ trait SQLConf {
   /** ************************ Spark SQL Params/Hints ******************* */
   // TODO: refactor so that these hints accessors don't pollute the name space of SQLContext?
 
+  /** When true tables cached using the in-memory columnar caching will be compressed. */
+  private[spark] def useCompression: Boolean = get(COMPRESS_CACHED, "false").toBoolean
+
   /** Number of partitions to use for shuffle operators. */
   private[spark] def numShufflePartitions: Int = get(SHUFFLE_PARTITIONS, "200").toInt
 

sql/core/src/main/scala/org/apache/spark/sql/SQLContext.scala

@@ -192,8 +192,6 @@ class SQLContext(@transient val sparkContext: SparkContext)
         currentTable.logicalPlan
 
       case _ =>
-        val useCompression =
-          sparkContext.conf.getBoolean("spark.sql.inMemoryColumnarStorage.compressed", false)
         InMemoryRelation(useCompression, executePlan(currentTable).executedPlan)
     }