MongoDB Table Design and Query Performance

Question

I'm new to MongoDB. When creating a new table a question came to my mind related to how to design it and performance. My table structure looks this way:

{
    "name" : string,
    "data" : { "data1" : "xxx", "data2" : "yyy", "data3" : "zzz", .... }           
}

The "data" field could grow until it reaches an amount of 100.000 elements ( "data100.000" : "aaaXXX"). However the number of rows in this table would be under control (between 500 and 1000).

This table will be accessed many times in my application and I'd like to maximize the performance of any queries. I would do queries like this one (I'll put an example in java):

new Query().addCriteria(Criteria.where("name").is(name).and("data.data3").is("zzz"));

I don't know if this would get slower when the amount of "dataX"... elements grows.

So the question is: Is this design correct? Should I change something?

I'll be pleased to read your advice, many thanks in advance

Answer 1

A document could be viewed like a table with columns, but you have to be carefull. It has other usage characteristics. The document size can be max. 16 MB. And you have to keep in mind that the documents are hold in memory by mongo.

With your query the whole document will be returned. Ask yourself do you need all entries or will you have to use a single entry on his own?

• Using MongoDB for eCommerce
• MongoDB Schema Design
• MongoDB and eCommerce
• MongoDB Transactions

This should be a good start.

Answer 2

What is data? I wouldn't store a single nested document with up to 100,000 fields as it you wouldn't be able to index it easily so you would get performance issues.

You'd be better off storing as an array of strings, then you can index the array field which would index all the values.

{
    "name" : string,
    "data" : [ "xxx", "yyy", "zzz" ]
}

If like in your query you then wanted the value at a particular position in the array, instead of data.data3 you could do:

db.Collection.find( { "data.2" : "zzz" } )

Or, if you don't care about the position and just want all documents where the data array contains 'zzz' you can do:

db.Collection.find( { "data" : "zzz" } )

100,000 strings is not going to get anywhere near 16MB so you don't need to worry about that, but having 100,000 fields in a nested document or array indicates something is wrong with the design, but without knowing what data is I couldn't say for sure.