[SPARK-7438] [SPARK CORE] Fixed validation of relativeSD in countAppr…

…oxDistinct

Author: Vinod K C <vinod.kc@huawei.com>

Closes apache#5974 from vinodkc/fix_countApproxDistinct_Validation and squashes the following commits:

3a3d59c [Vinod K C] Reverted removal of validation relativeSD<0.000017
799976e [Vinod K C] Removed testcase to assert IAE when relativeSD>3.7
8ddbfae [Vinod K C] Remove blank line
b1b00a3 [Vinod K C] Removed relativeSD validation from python API,RDD.scala will do validation
122d378 [Vinod K C] Fixed validation of relativeSD in  countApproxDistinct

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

@@ -1161,8 +1161,8 @@ abstract class RDD[T: ClassTag](
    */
   @Experimental
   def countApproxDistinct(p: Int, sp: Int): Long = withScope {
-    require(p >= 4, s"p ($p) must be at least 4")
-    require(sp <= 32, s"sp ($sp) cannot be greater than 32")
+    require(p >= 4, s"p ($p) must be >= 4")
+    require(sp <= 32, s"sp ($sp) must be <= 32")
     require(sp == 0 || p <= sp, s"p ($p) cannot be greater than sp ($sp)")
     val zeroCounter = new HyperLogLogPlus(p, sp)
     aggregate(zeroCounter)(
@@ -1187,8 +1187,9 @@ abstract class RDD[T: ClassTag](
    *                   It must be greater than 0.000017.
    */
   def countApproxDistinct(relativeSD: Double = 0.05): Long = withScope {
+    require(relativeSD > 0.000017, s"accuracy ($relativeSD) must be greater than 0.000017")
     val p = math.ceil(2.0 * math.log(1.054 / relativeSD) / math.log(2)).toInt
-    countApproxDistinct(p, 0)
+    countApproxDistinct(if (p < 4) 4 else p, 0)
   }
 
   /**

core/src/test/scala/org/apache/spark/rdd/RDDSuite.scala

@@ -89,6 +89,8 @@ class RDDSuite extends FunSuite with SharedSparkContext {
     val simpleRdd = sc.makeRDD(uniformDistro, 10)
     assert(error(simpleRdd.countApproxDistinct(8, 0), size) < 0.2)
     assert(error(simpleRdd.countApproxDistinct(12, 0), size) < 0.1)
+    assert(error(simpleRdd.countApproxDistinct(0.02), size) < 0.1)
+    assert(error(simpleRdd.countApproxDistinct(0.5), size) < 0.22)
   }
 
   test("SparkContext.union") {

python/pyspark/rdd.py

@@ -2239,8 +2239,6 @@ def countApproxDistinct(self, relativeSD=0.05):
         """
         if relativeSD < 0.000017:
             raise ValueError("relativeSD should be greater than 0.000017")
-        if relativeSD > 0.37:
-            raise ValueError("relativeSD should be smaller than 0.37")
         # the hash space in Java is 2^32
         hashRDD = self.map(lambda x: portable_hash(x) & 0xFFFFFFFF)
         return hashRDD._to_java_object_rdd().countApproxDistinct(relativeSD)

python/pyspark/tests.py

@@ -644,7 +644,6 @@ def test_count_approx_distinct(self):
         self.assertTrue(18 < rdd.map(lambda x: (x, -x)).countApproxDistinct() < 22)
 
         self.assertRaises(ValueError, lambda: rdd.countApproxDistinct(0.00000001))
-        self.assertRaises(ValueError, lambda: rdd.countApproxDistinct(0.5))
 
     def test_histogram(self):
         # empty