Link: Fast, easy, realtime metrics using Redis bitmaps To count unique users that logged in today, we set up a bitmap where each user is identified by an offset value. When a user visits a page or performs an action, which warrants it to be counted, set the bit to 1 at the offset representing user id.Redis のビットデータ型を使って、ユーザのアクティビティをカウント、集計する手法。 ユーザIDのオフセットにしてフラグをたてて、アグリゲートはpopulation count、複数のデータセッ