Yes. -Syyu is for "Sync (repository action), database update (forced), upgrade packages", in that order (though the flags don't have to be). Doubling a lowercase character like yy or uu is to force the operation. yy in particular shouldn't be needed, as it only overrides the "is your database recent" check. Unless you're updating more than every 5 minutes, using a single y is perfectly fine.
Yes. -Syyu is for "Sync (repository action), database update (forced), upgrade packages", in that order (though the flags don't have to be). Doubling a lowercase character like yy or uu is to force the operation. yy in particular shouldn't be needed, as it only overrides the "is your database recent" check. Unless you're updating more than every 5 minutes, using a single y is perfectly fine.