Github user cloud-fan commented on a diff in the pull request:
https://github.com/apache/spark/pull/22682#discussion_r223966211
--- Diff: docs/sql-programming-guide.md ---
@@ -1890,6 +1890,10 @@ working with timestamps in `pandas_udf`s to get the
best performance, see
# Migration Guide
+## Upgrading From Spark SQL 2.4 to 3.0
+
+ - In PySpark, when creating a `SparkSession` with
`SparkSession.builder.getOrCreate()`, if there is an existing `SparkContext`,
the builder was trying to update the `SparkConf` of the existing `SparkContext`
with configurations specified to the builder, but the `SparkContext` is shared
by all `SparkSession`s, so we should not update them. Since 3.0, the builder
come to not update the configurations. If you want to update them, you need to
update them prior to creating a `SparkSession`.
--- End diff --
let's also mention that, this is already the behavior for Spark java/scala
APIs.
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