"Sending read requests to secondaries is generally a bad idea. There are some specific situations in which it makes sense, but you should generally send all traffic to the primary." via Check out this quote from MongoDB: The Definitive Guide, 3rd Edition - https://learning.oreilly.com/library/view/mongodb-the-definitive/9781491954454/ch12.html
当たり前のようにSecondary Preferredを使っていたので衝撃を受けた。
