Assume that you run more than two PolyBase concurrent queries in SQL Server 2019. The query execution time may increase exponentially with the number of PolyBaseconcurrent queries. This situation is especially likely to happen with queries leveraging the compute pool in Big Data Clusters (BDCs), for example PolyBase Hadoop, Data Pool or Storage Pool queries.
Microsoft has confirmed that this is a problem in the Microsoft products that are listed in the "Applies to" section.
This issue is fixed in the following cumulative update for SQL Server:
About cumulative updates for SQL Server:
Each new cumulative update for SQL Server contains all the hotfixes and all the security fixes that were included with the previous cumulative update. Check out the latest cumulative updates for SQL Server: