Made the default cache BoundedMemoryCache, and reduced its default size

core/src/main/scala/spark/BoundedMemoryCache.scala

@@ -46,7 +46,7 @@ class BoundedMemoryCache extends Cache with Logging {
 
   private def getMaxBytes(): Long = {
     val memoryFractionToUse = System.getProperty(
-      "spark.boundedMemoryCache.memoryFraction", "0.75").toDouble
+      "spark.boundedMemoryCache.memoryFraction", "0.66").toDouble
     (Runtime.getRuntime.totalMemory * memoryFractionToUse).toLong
   }
 

core/src/main/scala/spark/SparkEnv.scala

@@ -21,7 +21,7 @@ object SparkEnv {
   }
 
   def createFromSystemProperties(isMaster: Boolean): SparkEnv = {
-    val cacheClass = System.getProperty("spark.cache.class", "spark.SoftReferenceCache")
+    val cacheClass = System.getProperty("spark.cache.class", "spark.BoundedMemoryCache")
     val cache = Class.forName(cacheClass).newInstance().asInstanceOf[Cache]
     
     val serializerClass = System.getProperty("spark.serializer", "spark.JavaSerializer")