Why is MongoDB taking too much time to find the record?

In this case, use the concept of index on a particular field. Let us first create a collection with documents. Here, we have created index as well using createIndex() −

> db.decreasetimeusingindex.createIndex({"StudentName":1});
{
   "createdCollectionAutomatically" : true,
   "numIndexesBefore" : 1,
   "numIndexesAfter" : 2,
   "ok" : 1
}
> db.decreasetimeusingindex.insertOne({"StudentName":"John Smith","StudentAge":21});
{
   "acknowledged" : true,
   "insertedId" : ObjectId("5e03960af5e889d7a51994ff")
}
> db.decreasetimeusingindex.insertOne({"StudentName":"John Doe","StudentAge":24});
{
   "acknowledged" : true,
   "insertedId" : ObjectId("5e039611f5e889d7a5199500")
}
> db.decreasetimeusingindex.insertOne({"StudentName":"Adam Smith","StudentAge":22});
{
   "acknowledged" : true,
   "insertedId" : ObjectId("5e03961df5e889d7a5199501")
}

Following is the query to display all documents from a collection with the help of find() method −

> db.decreasetimeusingindex.find().pretty();

This will produce the following output −

{
   "_id" : ObjectId("5e03960af5e889d7a51994ff"),
   "StudentName" : "John Smith",
   "StudentAge" : 21
}
{
   "_id" : ObjectId("5e039611f5e889d7a5199500"),
   "StudentName" : "John Doe",
   "StudentAge" : 24
}
{
   "_id" : ObjectId("5e03961df5e889d7a5199501"),
   "StudentName" : "Adam Smith",
   "StudentAge" : 22
}

Following is the query to find a specific record −

> db.decreasetimeusingindex.find({"StudentName":"Adam Smith"});

This will produce the following output −

{ "_id" : ObjectId("5e03961df5e889d7a5199501"), "StudentName" : "Adam Smith", "StudentAge" : 22 }