Assume that you enable the Multiple Active Result Sets (MARS) feature in Microsoft SQL Server 2014, and you set the max degree of parallelism (MAXDOP) option to a value of greater than 1. However, when you execute a parallel query that contains MERGE statements on clustered columnstore indexed tables through the MARS connection, you receive the following error message:
error 35377: When MARS is on, accessing clustered columnstore indexes is not allowed.
Note This issue does not occur when you set MAXDOP to 1.
The issue was first fixed in the following SQL Server cumulative updates:
Each new cumulative update for SQL Server contains all the hotfixes and security fixes that were included with the previous cumulative update. For the latest cumulative updates for SQL Server, see the following:
Microsoft has confirmed that this is a problem in the Microsoft products that are listed in the "Applies to" section.