Memory optimized DLLs not being cleaned up

Question

Hi,
From BOL, my understanding is that DBAs do not need to administer DLLs created for memory optimized tables, or natively compiled stored procedures, as they are recompiled automatically, when the SQL Server service starts and are removed when no longer needed.
But I am witnessing, that even after a memory optimized table has been dropped, and the service restarted, the DLLs still exist in the file system AND are still loaded into SQL memory and attached to the process. This can be witnessed by the fact that they
are still visible in sys_dm_os_loaded_modules, and are locked in the file system if you try to delete them, whilst the SQL Service is running.
Is this a bug? Or are they cleaned up at a later date? If at a later date, what triggers the clean-up, if it isn't an instance restart?
Pete

Answer 1

Most likely the DLLs are still needed during DB recovery, as there are still remnants of the tables in the checkpoint files. A couple of cycle of checkpoints and log truncation (e.g., by doing log backup) need to happen to clean up the old checkpoint
files and remove the remnants of the dropped tables from disk.
The following blog post details all the state transitions a checkpoint file goes through:
http://blogs.technet.com/b/dataplatforminsider/archive/2014/01/23/state-transition-of-checkpoint-files-in-databases-with-memory-optimized-tables.aspx