Storing Large JSON Object as JSON or as String?

Question

I have a large set of JSON docs which I am willing to store in a MongoDB.

However, given I am searching and retrieving only against few fields, I was wondering from performance-wise which way it would be better.

One option is to store the large object as JSON/BSON so the doc will look like:

{
    "key_1": "Value1",
    "key_2": "Value2",
    "external_data": {
        "large": {
            "data": [
                "comes",
                "here"
            ]
        }
    }
}

Or alternatively,

{
    "key_1": "Value1",
    "key_2": "Value2",
    "external_data": '{"large":{"data":["comes","here"]}}'
}

Answer 1

Interesting question, so i took the trouble to check it.

Sort answer is no significant performance difference in writes
here is the code i used for test it using pymongo driver along the results:

    docdict=dict(zip (["key" + str(i) for i in range (1,101)],[ "a"*i for i in range(1,101)]))
    docstr=str(docdict)
    def addIdtoStr(s,id):return {'_id':id,'payload':s} 
    def addIdtoDict(d,id): d.update({'_id':id});return d
    cProfile.run("for i in range(0,100000):x=dbcl.client.tests.test2.insert(addIdtoDict(docdict,i),w=0,j=0)")
     **12301152 function calls (12301128 primitive calls) in 56.089 second**
    dbcl.client.tests.test2.remove({},multi= True)
    cProfile.run("for i in range(0,100000):x=dbcl.client.tests.test2.insert(addIdStr(docstr,i),w=0,j=0)")
     **12201194 function calls (12115631 primitive calls) in 54.665 seconds**

Answer 2

I believe that storing the data in BSON is both performance and space-efficient. And by that you "invest" in future: if you store the data as BSON now, then it'll be possible to db-query it later if such requirement appears.

But anyway, if your concern is performance - you do have to profile it in the production environment, there is no way to tell that "it'll be faster or not".