How to know MongoDB collection size?

Question

I know that the below command will return the statistics regarding the collection:

db.collection.stats()

But in my output, my actual disk size is getting matched with the storage size. Refer to the below output:

    "count" : 20696445,

    "size" : NumberLong("1478263842661"),

    "storageSize" : 334732324864,

    "totalIndexSize" : 676327424,

    "indexSizes" : {

            "_id_" : 377094144,

            "leadID_1" : 128049152,

            "leadID_hashed" : 171184128

    },

    "avgObjSize" : 71425.97884134208

Can someone guide me what is the size for the other fields that are present inside the collection?

Answer 1

The output of the collection.stats() function will mainly depend on the version of the MongoDB server. In your code, you have not mentioned your MongoDB server version. I think you are working with WiredTiger Storage Engine as this storage engine will by default compress all your data and indexes that are present inside your collection. 

In the output, you are having 1.4TB of data(uncompressed) which is utilizing 334GB of the disk. In your indexSizes, the storage size that is being used by indexes is described separately.

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