Consider the following scenario:
- You have a Microsoft SQL Server 2016 database which contains columnstore indexes.
- You enable Read Committed Snapshot Isolation (RCSI) at database level, or the database is acting as a readable secondary replica in an Availability Group (RCSI is enabled by default in this case).
- You run read (SELECT) queries against columnstore index as INSERT statements occur on the same index.
In this scenario, you may notice poor performance in SQL Server 2016. Additionally, you may experience severe blocking and query waits on QUERY_TASK_ENQUEUE_MUTEX and ROWGROUP_VERSION.
As a workaround for this issue, you can drop the columnstore index on the table.
Microsoft has confirmed that this is a problem in the Microsoft products that are listed in the "Applies to" section.