3.9 came with strict DB requirements to enforce Barracuda file format, and people jumping in to upgrade or doing new installs are having trouble, as web hosting companies aren't ready for it yet, unless one have a dedicated server where they can play with anything they want to, I am not recommending upgrading to 3.9, even with control over everything let 3.9 become stable to jump ship.
3.9 came with strict DB requirements to enforce Barracuda file format, and people jumping in to upgrade or doing new installs are having trouble, as web hosting companies aren't ready for it yet, unless one have a dedicated server where they can play with anything they want to, I am not recommending upgrading to 3.9, even with control over everything let 3.9 become stable to jump ship.