Spark 2.0: Redefining SparkSession params through GetOrCreate and NOT seeing changes in WebUI

I believe that documentation is a bit misleading here and when you work with Scala you actually see a warning like this:

... WARN SparkSession$Builder: Use an existing SparkSession, some configuration may not take effect.

It was more obvious prior to Spark 2.0 with clear separation between contexts:

• SparkContext configuration cannot be modified on runtime. You have to stop existing context first.
• SQLContext configuration can be modified on runtime.

spark.app.name, like many other options, is bound to SparkContext, and cannot be modified without stopping the context.

Reusing existing SparkContext / SparkSession

import org.apache.spark.SparkConf
import org.apache.spark.sql.SparkSession

spark.conf.get("spark.sql.shuffle.partitions")

String = 200

val conf = new SparkConf()
  .setAppName("foo")
  .set("spark.sql.shuffle.partitions", "2001")

val spark = SparkSession.builder.config(conf).getOrCreate()

... WARN SparkSession$Builder: Use an existing SparkSession ...
spark: org.apache.spark.sql.SparkSession =  ...

spark.conf.get("spark.sql.shuffle.partitions")

String = 2001

While spark.app.name config is updated:

spark.conf.get("spark.app.name")

String = foo

it doesn't affect SparkContext:

spark.sparkContext.appName

String = Spark shell

Stopping existing SparkContext / SparkSession

Now let's stop the session and repeat the process:

spark.stop
val spark = SparkSession.builder.config(conf).getOrCreate()

...  WARN SparkContext: Use an existing SparkContext ...
spark: org.apache.spark.sql.SparkSession = ...

spark.sparkContext.appName

String = foo

Interestingly when we stop the session we still get a warning about using existing SparkContext, but you can check it is actually stopped.