Find largest document size in MongoDB?

To find the largest document size in MongoDB, you need to iterate through all documents in a collection and use the Object.bsonsize() function to calculate each document's size in bytes.

Syntax

var largestSize = 0;
db.collection.find().forEach(function(doc) {
    var currentSize = Object.bsonsize(doc);
    if (largestSize < currentSize) {
        largestSize = currentSize;
    }
});
print("Largest Document Size = " + largestSize);

Sample Data

Let us create a collection with documents of varying sizes ?

db.largestDocumentDemo.insertMany([
    {"StudentName": "John"},
    {
        "StudentName": "Carol",
        "StudentAge": 22,
        "StudentCountryName": "US",
        "TechnicalSubject": ["C", "C++", "Java", "MySQL"]
    },
    {"StudentName": "Mike", "StudentAge": 22}
]);

{
    "acknowledged": true,
    "insertedIds": [
        ObjectId("5c8ed2e32f684a30fbdfd57d"),
        ObjectId("5c8ed3282f684a30fbdfd57e"),
        ObjectId("5c8ed3382f684a30fbdfd57f")
    ]
}

Verify Sample Data

db.largestDocumentDemo.find().pretty();

{ "_id" : ObjectId("5c8ed2e32f684a30fbdfd57d"), "StudentName" : "John" }
{
    "_id" : ObjectId("5c8ed3282f684a30fbdfd57e"),
    "StudentName" : "Carol",
    "StudentAge" : 22,
    "StudentCountryName" : "US",
    "TechnicalSubject" : [
        "C",
        "C++",
        "Java",
        "MySQL"
    ]
}
{
    "_id" : ObjectId("5c8ed3382f684a30fbdfd57f"),
    "StudentName" : "Mike",
    "StudentAge" : 22
}

Find Largest Document Size

var largestDocumentSize = 0;
db.largestDocumentDemo.find().forEach(function(myObject) {
    var currentDocumentSize = Object.bsonsize(myObject);
    if (largestDocumentSize < currentDocumentSize) {
        largestDocumentSize = currentDocumentSize;
    }
});
print("The Largest Document Size = " + largestDocumentSize);

The Largest Document Size = 160

How It Works

• Object.bsonsize() returns the size of a document in bytes when stored in BSON format
• The forEach() method iterates through each document in the collection
• We compare each document size and store the largest value found

Conclusion

Use Object.bsonsize() with a forEach() loop to find the largest document size in a MongoDB collection. This method calculates the actual BSON storage size of each document and returns the maximum value in bytes.