Default NULL ordering change
The default NULL ordering changed from CDH to CDP. A workaround can prevent a possible performance hit.
Before Upgrade to CDP
In CDH, HIVE-20423 set NULLS LAST to be default ordering.
After Upgrade to CDP
In CDP, NULLS FIRST is the default ordering.
To prevent the change from affecting your workload performance, such as TopNKey operations, follow instructions in the Knowledge Base to set NULLS LAST as the default.