MongoDB 'count()' is very slow. How do we work around with it?

You can use ensureIndex() to boost the performance of count() method in MongoDB. To understand the concept, let us create a collection with the document. The query to create a collection with a document is as follows −

> db.countPerformanceDemo.insertOne({"StudentName":"John","StudentCountryName":"US"});
{
   "acknowledged" : true,
   "insertedId" : ObjectId("5c8ebcf82f684a30fbdfd55f")
}
> db.countPerformanceDemo.insertOne({"StudentName":"Mike","StudentCountryName":"UK"});
{
   "acknowledged" : true,
   "insertedId" : ObjectId("5c8ebd042f684a30fbdfd560")
}
> db.countPerformanceDemo.insertOne({"StudentName":"David","StudentCountryName":"AUS"});
{
   "acknowledged" : true,
   "insertedId" : ObjectId("5c8ebd112f684a30fbdfd561")
}
> db.countPerformanceDemo.insertOne({"StudentName":"Carol","StudentCountryName":"US"});
{
   "acknowledged" : true,
   "insertedId" : ObjectId("5c8ebd1a2f684a30fbdfd562")
}
> db.countPerformanceDemo.insertOne({"StudentName":"Bob","StudentCountryName":"UK"});
{
   "acknowledged" : true,
   "insertedId" : ObjectId("5c8ebd212f684a30fbdfd563")
}

> db.countPerformanceDemo.insertOne({"StudentName":"David","StudentCountryName":"UK"});
{
   "acknowledged" : true,
   "insertedId" : ObjectId("5c8ebd9a2f684a30fbdfd564")
}
> db.countPerformanceDemo.insertOne({"StudentName":"David","StudentCountryName":"US"});
{
   "acknowledged" : true,
   "insertedId" : ObjectId("5c8ebd9e2f684a30fbdfd565")
}

Display all documents from a collection with the help of find() method. The query is as follows −

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

The following is the output −

{
   "_id" : ObjectId("5c8ebcf82f684a30fbdfd55f"),
   "StudentName" : "John",
   "StudentCountryName" : "US"
}
{
   "_id" : ObjectId("5c8ebd042f684a30fbdfd560"),
   "StudentName" : "Mike",
   "StudentCountryName" : "UK"
}
{
   "_id" : ObjectId("5c8ebd112f684a30fbdfd561"),
   "StudentName" : "David",
   "StudentCountryName" : "AUS"
}
{
   "_id" : ObjectId("5c8ebd1a2f684a30fbdfd562"),
   "StudentName" : "Carol",
   "StudentCountryName" : "US"
}
{
   "_id" : ObjectId("5c8ebd212f684a30fbdfd563"),
   "StudentName" : "Bob",
   "StudentCountryName" : "UK"
}
{
   "_id" : ObjectId("5c8ebd9a2f684a30fbdfd564"),
   "StudentName" : "David",
   "StudentCountryName" : "UK"
}
{
   "_id" : ObjectId("5c8ebd9e2f684a30fbdfd565"),
   "StudentName" : "David",
   "StudentCountryName" : "US"
}

Here is the query to get the high-performance form of count() −

> db.countPerformanceDemo.ensureIndex({"StudentName":1});
{
   "createdCollectionAutomatically" : false,
   "numIndexesBefore" : 1,
   "numIndexesAfter" : 2,
   "ok" : 1
}

Now, implement count() method. It counts the records with StudentName “David”:

> db.countPerformanceDemo.find({"StudentName":"David"}).count();

The following is the output −

3