FIX: A deadlock occurs when you run a parallel query on a clustered columnstore index in SQL Server 2016 and 2017

Applies to: SQL Server 2016 DeveloperSQL Server 2016 EnterpriseSQL Server 2016 Enterprise Core


Consider the following scenario:

  • You execute a query in Microsoft SQL Server 2016 and 2017.
  • The resulting query plan contains a batch mode branch and a row mode branch involved in a JOIN.
  • In the row mode branch there are parallel and serial operators.

In this scenario, a deadlock condition might occur.

Note: This issue does not occur if you set the max degree of parallelism (MAXDOP) to 1 for the query.


This issue is fixed in the following cumulative updates for SQL Server:

       Cumulative Update 4 for SQL Server 2017

       Cumulative Update 7 for SQL Server 2016 SP1

Note The query optimizer hotfix trace flag (TF) 4199 must be enabled for this issue to be resolved. 

For more information about query optimizer hotfixes and trace flags, see:

SQL Server query optimizer hotfix TF 4199 servicing model

DBCC console commands and trace flags


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


Learn about the terminology that Microsoft uses to describe software updates.