What does "like pigs in clover" mean?

Extremely contentedly, as in They had a handsome pension and lived like pigs in clover. This expression alludes to pigs being allowed to eat as much clover, a favorite food, as they wish. It appeared in the Boston Gazette of January 7, 1813: “Canadians! then in droves come over, And live henceforth like pigs in clover.” [Early 1800s]