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

Well.. this is an old question.. but - I thought to share my cent about it

My approach - use Mongo mapReduce function

First - let's get the size for each document

db.myColection.mapReduce
(
   function() { emit(this._id, Object.bsonsize(this)) }, // map the result to be an id / size pair for each document
   function(key, val) { return val }, // val = document size value (single value for each document)
   { 
       query: {}, // query all documents
       out: { inline: 1 } // just return result (don't create a new collection for it)
   } 
)

This will return all documents sizes although it worth mentioning that saving it as a collection is a better approach (the result is an array of results inside the result field)

Second - let's get the max size of document by manipulating this query

db.metadata.mapReduce
(
    function() { emit(0, Object.bsonsize(this))}, // mapping a fake id (0) and use the document size as value
    function(key, vals) { return Math.max.apply(Math, vals) }, // use Math.max function to get max value from vals (each val = document size)
    { query: {}, out: { inline: 1 } } // same as first example
)

Which will provide you a single result with value equals to the max document size

In short:

you may want to use the first example and save its output as a collection (change out option to the name of collection you want) and applying further aggregations on it (max size, min size, etc.)

-OR-

you may want to use a single query (the second option) for getting a single stat (min, max, avg, etc.)