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mongodbdatabase-schema

Is shortening MongoDB property names worthwhile?

In mongodb docs the author mentions it's a good idea to shorten property names:

Use shorter field names.

and in an old blog post from how to node (it is offline by now April, 2022 edit)

....oft-reported issue with mongoDB is the size of the data on the disk... each and every record stores all the field-names .... This means that it can often be more space-efficient to have properties such as 't', or 'b' rather than 'title' or 'body', however for fear of confusion I would avoid this unless truly required!

I am aware of solutions of how to do it. I am more interested in when is this truly required?

Solution

  • I performed a little benchmark, I uploaded 252 rows of data from an Excel into two collections testShortNames and testLongNames as follows:

    Long Names:

    {
    "_id": ObjectId("6007a81ea42c4818e5408e9c"),
    "countryNameMaster": "Andorra",
    "countryCapitalNameMaster": "Andorra la Vella",
    "areaInSquareKilometers": 468,
    "countryPopulationNumber": NumberInt("77006"),
    "continentAbbreviationCode": "EU",
    "currencyNameMaster": "Euro"
}

    Short Names:

    {
    "_id": ObjectId("6007a81fa42c4818e5408e9d"),
    "name": "Andorra",
    "capital": "Andorra la Vella",
    "area": 468,
    "pop": NumberInt("77006"),
    "continent": "EU",
    "currency": "Euro"
}

    I then got the stats for each, saved in disk files, then did a "diff" on the two files:

    pprint.pprint(db.command("collstats", dbCollectionNameLongNames))

    The image below shows two variables of interest: size and storageSize. My reading showed that storageSize is the amount of disk space used after compression, and basically size is the uncompressed size. So we see the storageSize is identical. Apparently the Wired Tiger engine compresses fieldnames quite well. enter image description here

    I then ran a program to retrieve all data from each collection, and checked the response time.

    Even though it was a sub-second query, the long names consistently took about 7 times longer. It of course will take longer to send the longer names across from the database server to the client program.

    -------LongNames-------
Server Start DateTime=2021-01-20 08:44:38
Server End   DateTime=2021-01-20 08:44:39
StartTimeMs= 606964546  EndTimeM= 606965328
ElapsedTime MilliSeconds= 782
-------ShortNames-------
Server Start DateTime=2021-01-20 08:44:39
Server End   DateTime=2021-01-20 08:44:39
StartTimeMs= 606965328  EndTimeM= 606965421
ElapsedTime MilliSeconds= 93

    In Python, I just did the following (I had to actually loop through the items to force the reads, otherwise the query returns only the cursor):

    results = dbCollectionLongNames.find(query)
for result in results:
    pass