$in运算符是否有内置的记忆

这个 explain

PRIMARY> db.collection.explain().find({a:{$in:[1, 2, 2, 2, 3, 4]}}).next().queryPlanner

{
    "plannerVersion" : 1,
    "namespace" : "test.collection",
    "indexFilterSet" : false,
    "parsedQuery" : {
        "a" : {
            "$in" : [
                1,
                2,
                3,
                4
            ]
        }
    },
    "winningPlan" : {
        "stage" : "EOF"
    },
    "rejectedPlans" : [ ]
}