Get the size of list of documents in mongo db

Question

I want to get the size of the list of documents in mongodb.

db.getCollection('eventDetails').find({"dateTime" : { $gte : new ISODate("2018-05-01T12:00:00Z") },"dateTime" : { $lte : new ISODate("2018-05-31T23:59:59Z") }})

I want to get the size of the documents returned by the above mentioned query.

I tried the following query

var cursor = db.getCollection('eventDetails').find({"dateTime" : { $gte : new ISODate("2018-05-01T12:00:00Z") },"dateTime" : { $lte : new ISODate("2018-05-31T23:59:59Z") }})
var size = 0;
cursor.forEach(
    function(doc){
        size += Object.bsonsize(doc)
    }
);
print(size)

Each time execute the query, i get different results. Let me know how to get the size of the documents in mongodb

Answer 1

As per MongoDB jira blog documentation Real document size in collection and also MongoDB documentation here the Object.bsonsize(<document>) prints the BSON size of a <document> in bytes.

To find the size of all documents in a collection:

Object.bsonsize(db.collection.find( {dbname:"collectionname"}))

For Example

> use test
switched to db test
> db.createCollection("StackExchange");
{ "ok" : 1 }

> show collections
StackExchange
>

> db.StackExchange.insertOne({"Name" : "user3138864", "Password" : "abc123"})
{
        "acknowledged" : true,
        "insertedId" : ObjectId("5b740353194beb82d3752206")
}
> db.StackExchange.findOne()
{
        "_id" : ObjectId("5b740353194beb82d3752206"),
        "Name" : "user3138864",
        "Password" : "abc123"
}
> db.StackExchange.find().pretty()
{
        "_id" : ObjectId("5b740353194beb82d3752206"),
        "Name" : "user3138864",
        "Password" : "abc123"
}
> Object.bsonsize(db.StackExchange.find( {m040:"StackExchange"}))
45734

For further your ref here and here