what is the best practice for database design for high traffic websites like this one stackoverflow?

should one must use normalize database for record keeping or normalized technique or combination of both?

is it sensible to design normalize database as main database for record keeping to reduce redundancy and at the same time maintain another denormalized form of database for fast searching?

or

main database should be denormalize and one can make normalized views in the application level for fast database operations?

or beside above mentioned approach?

what is the best practice of designing high traffic websites???