Why Document DB ( like mongodb and couchdb ) are better for large amount of data?

Question

I am very newbie to this world of document db.

So... why this db are better than RDBMS ( like mysql or postgresql ) for very large amount of data ?

Answer 1

She have implement good indexing to carry this types of file, and this is designed for. This solution is better for Document Database, because is for it. Normal database is not designed to saving "documents", in this option you must hard work to search over your documents data, because each can be in other format this is a lot of work. If you choice document db solution you have all-in-one implemented because this database is for only "docuemnts", because this have implementation of these needed for it functions.

Answer 2

You want to distribute your data over multiple machines when you have a lot of data. That means that joins become really slow because joining between data on different machines means a lot of data communication between those machines.

You can store data in a mongodb/couchdb document in a hierarchical way so there is less need for joins.

But is is dependent on you use case(s). I think that relational databases do a better job when it comes to reporting.

MongoDB and CouchDB don't support transactions. Do you or your customers need transactions?

What do you want to do? Analyzing a lot of data (business intelligence/reporting) or a lot of small modifications per second "HVSP (High Volume Simple Processing)"?

• xRobot: I need to create a twitter-like application for my project at college and I have heard a lot about big company like Twitter, Google and Facebook that are using this document oriented db. When do you recommend document db ? only for join issue ? thanks ^_^
• TTT: I recommand that you start reading about the cap theorem, you could also start reading the sites "highscalability.com" and "nosql.mypopescu.com" and "www.dbms2.com". And the documentation of postgresql and mysql.