Hi all. I've been around here for a while but don't believe I've ever posted (I'm just a shy Northern bloke!) Thanks very much for your on going and valuable contributions.
Here's my offering to the current discussion, I hope it's useful...
Changing the compatibility level while users are connected to the database can produce incorrect result sets for active queries.
If the compatibility level changes while a query plan is being compiled, the compiled plan might be based on both the old and new compatibility levels, resulting in an incorrect plan and potentially inaccurate results.
The problem can then be further compounded if the plan is then placed in the plan cache and reused for subsequent queries.
The recommended procedure to change the compatibility level of a database is as follows:
- Set the database to single-user access mode.
- Change the compatibility level of the database.
- Put the database in multiuser access mode.
.. but do read the note of caution here...
https://msdn.microsoft.com/en-us/library/ms345598.aspx
In the short term, I think Capita could perhaps come up with a reworked migration tool for those yet to migrate and a patch, or series thereof, for those that have migrated. Changing Compatability mode can be an aid to migration but isn't putting things right at root.
Best regards.