[SPARK-15345][SQL][PYSPARK] SparkSession's conf doesn't take effect when this already an existing SparkContext

## What changes were proposed in this pull request?

Override the existing SparkContext is the provided SparkConf is different. PySpark part hasn't been fixed yet, will do that after the first round of review to ensure this is the correct approach.

## How was this patch tested?

Manually verify it in spark-shell.

rxin  Please help review it, I think this is a very critical issue for spark 2.0

Author: Jeff Zhang <zjffdu@apache.org>

Closes #13160 from zjffdu/SPARK-15345.

1 files changed, 3 insertions, 0 deletions

diff --git a/core/src/main/scala/org/apache/spark/SparkContext.scala b/core/src/main/scala/org/apache/spark/SparkContext.scala
index 36aa3becb4..5018eb38d9 100644
--- a/core/src/main/scala/org/apache/spark/SparkContext.scala
+++ b/core/src/main/scala/org/apache/spark/SparkContext.scala
@@ -2254,6 +2254,9 @@ object SparkContext extends Logging {
       if (activeContext.get() == null) {
         setActiveContext(new SparkContext(config), allowMultipleContexts = false)
       }
+      if (config.getAll.nonEmpty) {
+        logWarning("Use an existing SparkContext, some configuration may not take effect.")
+      }
       activeContext.get()
     }
   }