[SPARK-4047] - Generate runtime warnings for example implementation o…

…f PageRank

examples/src/main/python/pagerank.py

@@ -15,6 +15,11 @@
 # limitations under the License.
 #
 
+"""
+This is an example implementation of PageRank. For more conventional use,
+Please refer to PageRank implementation provided by graphx
+"""
+
 import re
 import sys
 from operator import add
@@ -40,6 +45,9 @@ def parseNeighbors(urls):
         print >> sys.stderr, "Usage: pagerank <file> <iterations>"
         exit(-1)
 
+    print >> sys.stderr,  """WARN: This is a naive implementation of PageRank and is
+          given as an example! Please refer to PageRank implementation provided by graphx"""
+
     # Initialize the spark context.
     sc = SparkContext(appName="PythonPageRank")
 

examples/src/main/scala/org/apache/spark/examples/SparkPageRank.scala

@@ -28,13 +28,28 @@ import org.apache.spark.{SparkConf, SparkContext}
  * URL         neighbor URL
  * ...
  * where URL and their neighbors are separated by space(s).
+ *
+ * This is an example implementation for learning how to use Spark. For more conventional use,
+ * please refer to org.apache.spark.graphx.lib.PageRank
  */
 object SparkPageRank {
+
+  def showWarning() {
+    System.err.println(
+      """WARN: This is a naive implementation of PageRank and is given as an example!
+        |Please use the PageRank implementation found in org.apache.spark.mllib.classification
+        |for more conventional use.
+      """.stripMargin)
+  }
+
   def main(args: Array[String]) {
     if (args.length < 1) {
       System.err.println("Usage: SparkPageRank <file> <iter>")
       System.exit(1)
     }
+
+    showWarning()
+
     val sparkConf = new SparkConf().setAppName("PageRank")
     val iters = if (args.length > 0) args(1).toInt else 10
     val ctx = new SparkContext(sparkConf)