[SPARK-5860][CORE] Prevent overflowing at the length level

Author: hotou

core/src/main/scala/org/apache/spark/rdd/JdbcRDD.scala

@@ -62,11 +62,11 @@ class JdbcRDD[T: ClassTag](
 
   override def getPartitions: Array[Partition] = {
     // bounds are inclusive, hence the + 1 here and - 1 on end
-    val length = 1 + BigInt(upperBound - lowerBound)
+    val length = BigInt(1) + upperBound - lowerBound
     (0 until numPartitions).map(i => {
-      val start = lowerBound + ((i * length) / numPartitions).toLong
-      val end = lowerBound + (((i + 1) * length) / numPartitions).toLong - 1
-      new JdbcPartition(i, start, end)
+      val start = lowerBound + ((i * length) / numPartitions)
+      val end = lowerBound + (((i + 1) * length) / numPartitions) - 1
+      new JdbcPartition(i, start.toLong, end.toLong)
     }).toArray
   }