mongodb: will limit() increase query speed?

Question

Is db.inventory.find().limit(10) faster than db.inventory.find()?

I have millions of records in mongodb, I want to get top 10 records in so

Answer 1

if you need it in order then of course the DB would first sort it based on the criteria and then return the top 10 records. by using the limit you are just saving the network bandwidth. e.g. here I am sorting by name and then giving the top 10 records, it has to scan the whole data and then pick the top 10. (as you can notice its doing COLLSCAN which is understood for collection scan as I don't have the index for this example, the idea to show here is that its doing the full scan of all the records, sort it and then pick the top ones.)

> db.t1.find().sort({name:1}).limit(10).explain()
{
    "queryPlanner" : {
            "plannerVersion" : 1,
            "namespace" : "test.t1",
            "indexFilterSet" : false,
            "parsedQuery" : {
                    "$and" : [ ]
            },
            "winningPlan" : {
                    "stage" : "SORT",
                    "sortPattern" : {
                            "name" : 1
                    },
                    "limitAmount" : 10,
                    "inputStage" : {
                            "stage" : "COLLSCAN",
                            "filter" : {
                                    "$and" : [ ]
                            },
                            "direction" : "forward"
                    }
            },
            "rejectedPlans" : [ ]
    },
    "serverInfo" : {
            "host" : "Sachin-Mac.local",
            "port" : 27017,
            "version" : "3.0.2",
            "gitVersion" : "6201872043ecbbc0a4cc169b5482dcf385fc464f"
    },
    "ok" : 1
}