This is a quick, perhaps Level 200 post – a rarity on my blog but I am seeing this so often that I think it important to get this out there.
Those who are running databases with compatibility level 90 in SQL Server 2008 / 2012 need to be aware that there is no more support for level 90 in SQL Server 2014. The SSMS 2014 UI is a bit confusing in this respect, because it does show you the option to set level as 90:
But when you try to actually change this to 90, it fails:
Msg 15048, Level 16, State 3, Line 1
Valid values of the database compatibility level are 100, 110, or 120.
Msg 5069, Level 16, State 1, Line 1
ALTER DATABASE statement failed.
This information is indeed documented in Books Online: “When a database is upgraded to SQL Server 2014 from any earlier version of SQL Server, the database retains its existing compatibility level if it is at least 100. Upgrading a database with a compatibility level of 90 sets the database to compatibility level 100. “
Call to action to everyone who plans to upgrade to SQL Server 2014 and is running a database on compatibility level 90 is to thoroughly test with compatibility level as 120 (or perhaps 110 if you feel the changes in the cardinality estimator will warrant more testing in your workload case) before you upgrade. Both functional and stress testing must be done. Once the testing is signed off, you can confidently do the upgrade in production with the higher compatibility levels – 120 (recommended; subject to testing outcome) or 110.
My team of Premier Field Engineers within Microsoft Services can also be of help to your upgrade efforts and help detect and mitigate risks related to upgrading to the current version. Do engage us if you need help!