In MongoDB, is using $in search faster than multiple single searches?

Yes, using $in is faster. Let us see an example and create a collection with documents −

> db.demo653.insertOne({subject:"MySQL"}); {    "acknowledged" : true,    "insertedId" : ObjectId("5ea04b274deddd72997713c0") } > db.demo653.insertOne({subject:"MongoDB"}); {    "acknowledged" : true,    "insertedId" : ObjectId("5ea04b304deddd72997713c1") } > db.demo653.insertOne({subject:"Java"}); {    "acknowledged" : true,    "insertedId" : ObjectId("5ea04b354deddd72997713c2") } > db.demo653.insertOne({subject:"C"}); {    "acknowledged" : true,    "insertedId" : ObjectId("5ea04b384deddd72997713c3") } > db.demo653.insertOne({subject:"C++"}); {    "acknowledged" : true,    "insertedId" : ObjectId("5ea04b3b4deddd72997713c4") }

Display all documents from a collection with the help of find() method −

> db.demo653.find();

This will produce the following output −

{ "_id" : ObjectId("5ea04b274deddd72997713c0"), "subject" : "MySQL" } { "_id" : ObjectId("5ea04b304deddd72997713c1"), "subject" : "MongoDB" } { "_id" : ObjectId("5ea04b354deddd72997713c2"), "subject" : "Java" } { "_id" : ObjectId("5ea04b384deddd72997713c3"), "subject" : "C" } { "_id" : ObjectId("5ea04b3b4deddd72997713c4"), "subject" : "C++" }

Following is the query to use $in and search faster than multiple single searches −

> db.demo653.find({subject:{$in:["MySQL","C++","C"]}});

This will produce the following output −

{ "_id" : ObjectId("5ea04b274deddd72997713c0"), "subject" : "MySQL" } { "_id" : ObjectId("5ea04b384deddd72997713c3"), "subject" : "C" } { "_id" : ObjectId("5ea04b3b4deddd72997713c4"), "subject" : "C++" }