main.go

package main

import (
	"context"
	"fmt"
	"log"
	"strings"

	"go.mongodb.org/mongo-driver/bson"
	"go.mongodb.org/mongo-driver/mongo"
	"go.mongodb.org/mongo-driver/mongo/options"
)

// Generates a document of the form {_id: X, key: Y} where the total
// document size is equal to 16 MiB. Generates a long string for Y in
// order to reach 16 MiB.
func generate16MiBDocument() bson.M {
	// Here's a breakdown of bytes in the document:
	//
	// 4 bytes = document length
	// 1 byte = element type (ObjectID = \x07)
	// 4 bytes = key name ("_id" + \x00)
	// 12 bytes = ObjectID value
	// 1 byte = element type (string = \x02)
	// 4 bytes = key name ("key" + \x00)
	// 4 bytes = string length
	// X bytes = string of length X bytes
	// 1 byte = \x00
	// 1 byte = \x00
	//
	// Therefore the string length should be: 1024*1024*16 - 32
	// Note, _id is added on the server

	var b strings.Builder

	size := 1024*1024*16 - 32

	b.Grow(size)
	for i := 0; i < size; i++ {
		b.WriteByte(byte('A'))
	}

	return bson.M{"key": b.String()}
}

func main() {
	// Set client options
	clientOptions := options.Client().ApplyURI("mongodb://localhost:27017/test")

	// Connect to MongoDB
	client, err := mongo.Connect(context.TODO(), clientOptions)

	if err != nil {
		log.Fatal(err)
	}

	largeDoc := generate16MiBDocument()

	_, err = client.Database("foo").Collection("bar").InsertOne(context.Background(), largeDoc)

	if err != nil {
		fmt.Printf("ERROR: %v\n\n", err)
	} else {
		fmt.Print("Successfully inserted document")
	}
}