FIX: Parallel query execution plan with "merge join" slow to execute in Cumulative Update 3, 4, or 5 for SQL Server 2016 Service Pack 1

Applies to: SQL Server 2016 Enterprise CoreSQL Server 2016 EnterpriseSQL Server 2016 Developer More

Symptoms


When you use Cumulative Update 3, Cumulative Update 4, or Cumulative Update 5 for SQL Server 2016 Service Pack 1, a query that uses a parallel query execution plan that contains a merge join operator may take longer to execute with extremely skewed data.

Resolution


This fix is included in the following cumulative updates for SQL Server: 

Cumulative Update 2 for SQL Server 2017

Cumulative Update 6 for SQL Server 2016 SP1

Status


Microsoft has confirmed that this is a problem in the Microsoft products that are listed in the "Applies to" section.

References


Learn about the terminology Microsoft uses to describe software updates.