[SPARK-19693][SQL] Make the SET mapreduce.job.reduces automatically converted...

[SPARK-19693][SQL] Make the SET mapreduce.job.reduces automatically converted to spark.sql.shuffle.partitions

## What changes were proposed in this pull request?
Make the `SET mapreduce.job.reduces` automatically converted to `spark.sql.shuffle.partitions`, it's similar to `SET mapred.reduce.tasks`.

## How was this patch tested?

unit tests

Author: Yuming Wang <wgyumg@gmail.com>

Closes #17020 from wangyum/SPARK-19693.

sql/core/src/main/scala/org/apache/spark/sql/execution/command/SetCommand.scala

@@ -60,6 +60,23 @@ case class SetCommand(kv: Option[(String, Option[String])]) extends RunnableComm
       }
       (keyValueOutput, runFunc)
 
+    case Some((SQLConf.Replaced.MAPREDUCE_JOB_REDUCES, Some(value))) =>
+      val runFunc = (sparkSession: SparkSession) => {
+        logWarning(
+          s"Property ${SQLConf.Replaced.MAPREDUCE_JOB_REDUCES} is Hadoop's property, " +
+            s"automatically converted to ${SQLConf.SHUFFLE_PARTITIONS.key} instead.")
+        if (value.toInt < 1) {
+          val msg =
+            s"Setting negative ${SQLConf.Replaced.MAPREDUCE_JOB_REDUCES} for automatically " +
+              "determining the number of reducers is not supported."
+          throw new IllegalArgumentException(msg)
+        } else {
+          sparkSession.conf.set(SQLConf.SHUFFLE_PARTITIONS.key, value)
+          Seq(Row(SQLConf.SHUFFLE_PARTITIONS.key, value))
+        }
+      }
+      (keyValueOutput, runFunc)
+
     case Some((key @ SetCommand.VariableName(name), Some(value))) =>
       val runFunc = (sparkSession: SparkSession) => {
         sparkSession.conf.set(name, value)

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

@@ -677,6 +677,10 @@ object SQLConf {
   object Deprecated {
     val MAPRED_REDUCE_TASKS = "mapred.reduce.tasks"
   }
+
+  object Replaced {
+    val MAPREDUCE_JOB_REDUCES = "mapreduce.job.reduces"
+  }
 }
 
 /**

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

@@ -1019,6 +1019,18 @@ class SQLQuerySuite extends QueryTest with SharedSQLContext {
     spark.sessionState.conf.clear()
   }
 
+  test("SET mapreduce.job.reduces automatically converted to spark.sql.shuffle.partitions") {
+    spark.sessionState.conf.clear()
+    val before = spark.conf.get(SQLConf.SHUFFLE_PARTITIONS.key).toInt
+    val newConf = before + 1
+    sql(s"SET mapreduce.job.reduces=${newConf.toString}")
+    val after = spark.conf.get(SQLConf.SHUFFLE_PARTITIONS.key).toInt
+    assert(before != after)
+    assert(newConf === after)
+    intercept[IllegalArgumentException](sql(s"SET mapreduce.job.reduces=-1"))
+    spark.sessionState.conf.clear()
+  }
+
   test("apply schema") {
     val schema1 = StructType(
       StructField("f1", IntegerType, false) ::