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