[SPARK-15726][SQL] Make DatasetBenchmark fairer among Dataset, DataFrame and RDD

## What changes were proposed in this pull request?

DatasetBenchmark compares the performances of RDD, DataFrame and Dataset while running the same operations. However, there are two problems that make the comparisons unfair.

1) In backToBackMap test case, only DataFrame implementation executes less work compared to RDD or Dataset implementations. This test case processes Long+String pairs, but the output from the DataFrame implementation does not include String part while RDD or Dataset generates Long+String pairs as output. This difference significantly changes the performance characteristics due to the String manipulation and creation overheads.

2) In back-to-back map and back-to-back filter test cases, `map` or `filter` operation is executed only once regardless of `numChains` parameter for RDD. Hence the execution times for RDD have been largely underestimated.

Of course, these issues do not affect Spark users, but it may confuse Spark developers.

## How was this patch tested?
By executing the DatasetBenchmark

Author: Hiroshi Inoue <inouehrs@jp.ibm.com>

Closes #13459 from inouehrs/fix_benchmark_fairness.

sql/core/src/test/scala/org/apache/spark/sql/DatasetBenchmark.scala

@@ -43,7 +43,7 @@ object DatasetBenchmark {
       var res = rdd
       var i = 0
       while (i < numChains) {
-        res = rdd.map(func)
+        res = res.map(func)
         i += 1
       }
       res.foreach(_ => Unit)
@@ -53,7 +53,7 @@ object DatasetBenchmark {
       var res = df
       var i = 0
       while (i < numChains) {
-        res = res.select($"l" + 1 as "l")
+        res = res.select($"l" + 1 as "l", $"s")
         i += 1
       }
       res.queryExecution.toRdd.foreach(_ => Unit)
@@ -87,7 +87,7 @@ object DatasetBenchmark {
       var res = rdd
       var i = 0
       while (i < numChains) {
-        res = rdd.filter(funcs(i))
+        res = res.filter(funcs(i))
         i += 1
       }
       res.foreach(_ => Unit)
@@ -170,36 +170,36 @@ object DatasetBenchmark {
     val benchmark3 = aggregate(spark, numRows)
 
     /*
-    Java HotSpot(TM) 64-Bit Server VM 1.8.0_60-b27 on Mac OS X 10.11.4
-    Intel(R) Core(TM) i7-4960HQ CPU @ 2.60GHz
-    back-to-back map:                   Best/Avg Time(ms)    Rate(M/s)   Per Row(ns)   Relative
-    -------------------------------------------------------------------------------------------
-    RDD                                      1935 / 2105         51.7          19.3       1.0X
-    DataFrame                                 756 /  799        132.3           7.6       2.6X
-    Dataset                                  7359 / 7506         13.6          73.6       0.3X
+    OpenJDK 64-Bit Server VM 1.8.0_91-b14 on Linux 3.10.0-327.18.2.el7.x86_64
+    Intel Xeon E3-12xx v2 (Ivy Bridge)
+    back-to-back map:                        Best/Avg Time(ms)    Rate(M/s)   Per Row(ns)   Relative
+    ------------------------------------------------------------------------------------------------
+    RDD                                           3448 / 3646         29.0          34.5       1.0X
+    DataFrame                                     2647 / 3116         37.8          26.5       1.3X
+    Dataset                                       4781 / 5155         20.9          47.8       0.7X
     */
     benchmark.run()
 
     /*
-    Java HotSpot(TM) 64-Bit Server VM 1.8.0_60-b27 on Mac OS X 10.11.4
-    Intel(R) Core(TM) i7-4960HQ CPU @ 2.60GHz
-    back-to-back filter:                Best/Avg Time(ms)    Rate(M/s)   Per Row(ns)   Relative
-    -------------------------------------------------------------------------------------------
-    RDD                                      1974 / 2036         50.6          19.7       1.0X
-    DataFrame                                 103 /  127        967.4           1.0      19.1X
-    Dataset                                  4343 / 4477         23.0          43.4       0.5X
+    OpenJDK 64-Bit Server VM 1.8.0_91-b14 on Linux 3.10.0-327.18.2.el7.x86_64
+    Intel Xeon E3-12xx v2 (Ivy Bridge)
+    back-to-back filter:                     Best/Avg Time(ms)    Rate(M/s)   Per Row(ns)   Relative
+    ------------------------------------------------------------------------------------------------
+    RDD                                           1346 / 1618         74.3          13.5       1.0X
+    DataFrame                                       59 /   72       1695.4           0.6      22.8X
+    Dataset                                       2777 / 2805         36.0          27.8       0.5X
     */
     benchmark2.run()
 
     /*
-    Java HotSpot(TM) 64-Bit Server VM 1.8.0_60-b27 on Mac OS X 10.11.4
-    Intel(R) Core(TM) i7-4960HQ CPU @ 2.60GHz
-    aggregate:                          Best/Avg Time(ms)    Rate(M/s)   Per Row(ns)   Relative
-    -------------------------------------------------------------------------------------------
-    RDD sum                                  2130 / 2166         46.9          21.3       1.0X
-    DataFrame sum                              92 /  128       1085.3           0.9      23.1X
-    Dataset sum using Aggregator             4111 / 4282         24.3          41.1       0.5X
-    Dataset complex Aggregator               8782 / 9036         11.4          87.8       0.2X
+    OpenJDK 64-Bit Server VM 1.8.0_91-b14 on Linux 3.10.0-327.18.2.el7.x86_64
+    Intel Xeon E3-12xx v2 (Ivy Bridge)
+    aggregate:                               Best/Avg Time(ms)    Rate(M/s)   Per Row(ns)   Relative
+    ------------------------------------------------------------------------------------------------
+    RDD sum                                       1420 / 1523         70.4          14.2       1.0X
+    DataFrame sum                                   31 /   49       3214.3           0.3      45.6X
+    Dataset sum using Aggregator                  3216 / 3257         31.1          32.2       0.4X
+    Dataset complex Aggregator                    7948 / 8461         12.6          79.5       0.2X
     */
     benchmark3.run()
   }