modify according to comments

python/pyspark/sql/dataframe.py

@@ -272,7 +272,7 @@ def isLocal(self):
         """
         return self._jdf.isLocal()
 
-    def show(self, numRows=20):
+    def show(self, n=20):
         """
         Print the first n rows.
 
@@ -283,7 +283,7 @@ def show(self, numRows=20):
         2   Alice
         5   Bob
         """
-        print self._jdf.showString(numRows).encode('utf8', 'ignore')
+        print self._jdf.showString(n).encode('utf8', 'ignore')
 
     def __repr__(self):
         return "DataFrame[%s]" % (", ".join("%s: %s" % c for c in self.dtypes))

sql/core/src/main/scala/org/apache/spark/sql/DataFrame.scala

@@ -161,9 +161,8 @@ class DataFrame protected[sql](
    * Internal API for Python
    * @param numRows Number of rows to show
    */
-  private[sql] def showString(numRows: Int = 20): String = {
-    val size = count()
-    val data = if (numRows > size) collect() else take(numRows)
+  private[sql] def showString(numRows: Int): String = {
+    val data = take(numRows)
     val numCols = schema.fieldNames.length
 
     // For cells that are beyond 20 characters, replace it with the first 17 and "..."

sql/core/src/test/java/test/org/apache/spark/sql/JavaDataFrameSuite.java

@@ -81,4 +81,11 @@ public void testVarargMethods() {
     df.groupBy().agg(countDistinct(col("key"), col("value")));
     df.select(coalesce(col("key")));
   }
+
+  @Test
+  public void testShow() {
+    DataFrame df = context.table("testData");
+    df.show(10);
+    df.show(1000);
+  }
 }

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

@@ -441,4 +441,8 @@ class DataFrameSuite extends QueryTest {
     checkAnswer(df.select(df("key")), testData.select('key).collect().toSeq)
   }
 
+  test("show") {
+    testData.select($"*").show()
+    testData.select($"*").show(1000)
+  }
 }