reset threshold values for doStack and remove UT

Author: hqzizania

mllib/src/main/scala/org/apache/spark/ml/recommendation/ALS.scala

@@ -1325,7 +1325,7 @@ object ALS extends DefaultParamsReadable[ALS] with Logging {
           var numExplicits = 0
           // Stacking factors(vectors) in matrices to speed up the computation,
           // when the number of factors and the rank is large enough.
-          val doStack = srcPtrs(j + 1) - srcPtrs(j) > 128 && rank > 128
+          val doStack = srcPtrs(j + 1) - srcPtrs(j) > 1024 && rank > 1024
           val srcFactorBuffer = mutable.ArrayBuilder.make[Double]
           val bBuffer = mutable.ArrayBuilder.make[Double]
           while (i < srcPtrs(j + 1)) {

mllib/src/test/scala/org/apache/spark/ml/recommendation/ALSSuite.scala

@@ -389,11 +389,6 @@ class ALSSuite
       targetRMSE = 0.3)
   }
 
-  test("rank-129 matrix with stacking factors in matrices") {
-    val (training, test) = genExplicitTestData(numUsers = 200, numItems = 20, rank = 1)
-    testALS(training, test, maxIter = 1, rank = 129, regParam = 0.01, targetRMSE = 0.02)
-  }
-
   test("using generic ID types") {
     val (ratings, _) = genImplicitTestData(numUsers = 20, numItems = 40, rank = 2, noiseStd = 0.01)