How to get the size of single document in Mongodb?

javascript mongodb document objectid objectsize

105,587

Solution 1

In the previous call of Object.bsonsize(), Mongodb returned the size of the cursor, rather than the document.

Correct way is to use this command:

Object.bsonsize(db.test.findOne())

With findOne(), you can define your query for a specific document:

Object.bsonsize(db.test.findOne({type:"auto"}))

This will return the correct size (in bytes) of the particular document.

Solution 2

MAXIMUM DOCUMENT SIZE 16 MiB (source)

If you have version >=4.4 ($bsonSize source)

db.users.aggregate([
  {
    "$project": {
      "size_bytes": { "$bsonSize": "$$ROOT" },
      "size_KB": { "$divide": [{"$bsonSize": "$$ROOT"}, 1000] },
      "size_MB": { "$divide": [{"$bsonSize": "$$ROOT"}, 1000000] }
    }
  }
])

If you have version <4.4 (Object.bsonSize() source)

You can use this script for get a real size:

db.users.find().forEach(function(obj)
{
  var size = Object.bsonsize(obj);
  print('_id: '+obj._id+' || Size: '+size+'B -> '+Math.round(size/(1000))+'KB -> '+Math.round(size/(1000*1000))+'MB (max 16MB)');
});

Note: If your IDs are 64-bit integers, the above will truncate the ID value on printing! If that's the case, you can use instead:

db.users.find().forEach(function(obj)
{
  var size = Object.bsonsize(obj);
  var stats =
  {
    '_id': obj._id, 
    'bytes': size, 
    'KB': Math.round(size/(1000)), 
    'MB': Math.round(size/(1000*1000))
  };
  print(stats);
});

This also has the advantage of returning JSON, so a GUI like RoboMongo can tabulate it!

edit : thanks to @zAlbee for your suggest completion.

Solution 3

The effective amount of space the document will take in the collection will be more than the size of your document because of the Record Padding mechanism.

This is why there is a difference between the outputs of the db.test.stats() and Object.bsonsize(..).

To get the exact size (in bytes) of the document, stick to the Object.bsonsize() function.

Solution 4

With mongodb 4.4 (upcoming), You can use bsonSize operator to get the document size.

db.test.aggregate([
  {
    "$project": {
      "name": 1,
      "object_size": { "$bsonSize": "$$ROOT" }
    }
  }
])

Solution 5

Object.bsonsize(db.test.findOne({type:"auto"})) It gives in bytes.

View more solutions

105,587

user1949763

Updated on January 17, 2022

Comments

user1949763 over 2 years
I encountered a strange behavior of mongo and I would like to clarify it a bit...
My request is simple as that: I would like to get a size of single document in collection. I found two possible solutions:
- Object.bsonsize - some javascript method that should return a size in bytes
- db.collection.stats() - where there is a line 'avgObjSize' that produce some "aggregated"(average) size view on the data. It simply represents average size of single document.
Here, I provide some code I perform testing on:
1. I created new database 'test' and input simple document with only one attribute: type:"auto"
```
db.test.insert({type:"auto"})
```
2. output from stats() function call: db.test.stats():
```
{ 
  "ns" : "test.test",
  "count" : 1,
  "size" : 40,
  "avgObjSize" : 40,
  "storageSize" : 4096,
  "numExtents" : 1,
  "nindexes" : 1,
  "lastExtentSize" : 4096,
  "paddingFactor" : 1,
  "systemFlags" : 1,
  "userFlags" : 0,
  "totalIndexSize" : 8176,
  "indexSizes" : {
        "_id_" : 8176
},
"ok" : 1
```
  }
3. output from bsonsize function call: Object.bsonsize(db.test.find({test:"auto"}))
```
481
```
user1949763 over 10 years

Thank you for your reply, in that case, I have another question regarding this issue: suppose I have a collection where documents with long list of identifiers are saved in the form of the list. (identifiers are stored originally in txt-csv file- with size 300 kB; each identifier is 10characters long) When I run bsonsize on such a document the size is even lower than 481. It returns 465. Could you explain to me this situation, please?
John Evans over 9 years

Which size is used to enforce the mongDB document size limitation? Object.bsonsize()?
leon over 8 years

How to get the size of a list of document with query?
Sercan Ozdemir over 8 years

But of course this code will fetch the document before calculating the size.
htm11h over 8 years

The MongoDB document size is a constraint of the Mongo, this is covered in the manual on their web site, 16MB. I have hit this limit a number of times trying import records.
Liberateur over 7 years

This not return a goood size :(... But this : stackoverflow.com/a/40993183/3933634
Erce over 5 years

This is exactly what i am looking for but it not working maybe related with my mongo version. current one is 3.4 ?
PARAMANANDA PRADHAN over 5 years

How to get Object.bsonsize, what is the import or required statement?
Félix Paradis over 5 years

Anyone else getting TypeError: Object.bsonsize is not a function ?
Liberateur over 5 years

Do you have try in mongo shell ? It's work : docs.mongodb.com/manual/reference/mongo-shell/#miscellaneous
Sam about 5 years

For anyone else who missed it, you must use findOne instead of find
Emmanuel Mtali over 4 years

Try to explain your answer . .
Wernfried Domscheit almost 4 years

Proper label would be rather 'KiB': Math.round(size/(1024)), 'MiB': Math.round(size/(1024*1024)) (or 'kB': Math.round(size/(1000)), 'MB': Math.round(size/(1000*1000))
Luk Aron over 3 years

how to do it in python?
Wernfried Domscheit over 2 years

For anyone else who missed it, you must use findOne or find().toArray() instead of find Using find().toArray() of course gives the size sum of all documents.