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If you don't already have a second 2012 license, you should buy one now, add a second DC to the network as a VM on the same system, transfer the roles off it, then demote the physical DC and make it so it ONLY runs Hyper-V.
You should limit the amount of RAM the Windows Internal Database can use. Follow directions here to limit the RAM
http://www.stugr.com/2013/01/wsus-limit-sql-windows-internal-database-memory/
(Copied from above link for command line method; GUI method in link).
Open a cmd window
Enter the following command depending on version:
For WSUS 4 (Server 2012:
osql -E -S \\.\pipe\Microsoft##WID\ts
For WSUS 3:
osql -E -S \\.\pipe\mssql$microsoft##
Enter the following commands:
exec sp_configure 'show advanced option', '1';
reconfigure;
To view currently set max server memory:
exec sp_configure;
go
To reconfigure:
exec sp_configure 'max server memory', 2048;
reconfigure with override;
go
quit
Restart the SQL service