What is the *.VC.db file in Visual Studio projects?

In some Visual Studio 2015 projects that I have, there is a *.VC.db file in the project folder, named after the project: If the project name is FooBar, then the file is FooBar.VC.db.

This file looks like a database of some sort, but I'm not using any databases at all in the projects.

My best guess would be that it is operating similarly than the HelloWorld.sdf database, which is used by IntelliSense.

Is it the same just in "new", or is it doing something important and I shouldn't delete it?

This happens after you installed VS2015 Update 2. The projname.vc.db file is the new IntelliSense database, it replaces the old projname.sdf database. Not otherwise by deleting that .sdf file. You may also see a hidden projname.vc.vc.opendb file, a lock file to indicate that the dbase is in use. Crystal ball says that somebody is bound to have to delete this one by hand sooner or later.

This was already available before but was experimental. Now permanent. Promises are for a rough x2 speedup of IntelliSense. Biggest change appears to be switching to another dbase engine, now using SQLite instead of SQL Compact. Powerful open source confidence vote there :)

Don't delete the file just yet or next time you open the project IS is going to be catatonic for a while. Well, not as long as before :) You'd consider cleanup, if at all, when you're done with the project. Go ahead and delete the .sdf file, it will no longer be used.