Disable compression by default

Author: liancheng

sql/core/src/main/scala/org/apache/spark/sql/columnar/compression/CompressionScheme.scala

@@ -57,8 +57,14 @@ private[sql] trait AllCompressionSchemes extends WithCompressionSchemes {
 }
 
 private[sql] object CompressionScheme {
-  val all: Seq[CompressionScheme] =
+  val compressionEnabled =
+    System.getProperty("spark.sql.inMemoryCompression.enabled", "false").toBoolean
+
+  val all: Seq[CompressionScheme] = if (compressionEnabled) {
     Seq(PassThrough, RunLengthEncoding, DictionaryEncoding, BooleanBitSet, IntDelta, LongDelta)
+  } else {
+    Seq(PassThrough)
+  }
 
   private val typeIdToScheme = all.map(scheme => scheme.typeId -> scheme).toMap