Find largest document size in MongoDB

Question

Is it possible to find the largest document size in MongoDB?

db.collection.stats() shows average size, which is not really representative because in my

Answer 1

Starting Mongo 4.4, the new aggregation operator $bsonSize returns the size in bytes of a given document when encoded as BSON.

Thus, in order to find the bson size of the document whose size is the biggest:

// { "_id" : ObjectId("5e6abb2893c609b43d95a985"), "a" : 1, "b" : "hello" }
// { "_id" : ObjectId("5e6abb2893c609b43d95a986"), "c" : 1000, "a" : "world" }
// { "_id" : ObjectId("5e6abb2893c609b43d95a987"), "d" : 2 }
db.collection.aggregate([
  { $group: {
    _id: null,
    max: { $max: { $bsonSize: "$$ROOT" } }
  }}
])
// { "_id" : null, "max" : 46 }

This:

• $groups all items together
• $projects the $max of documents' $bsonSize
• $$ROOT represents the current document for which we get the bsonsize