couchdb multiple databases

Question

I'm used to working with mysql but for my next series of projects CouchDB (NoSQL) seems to be the way to go, basically to avoid EAV in mysql and to embrace all the cool features it has to offer.

After lots of investigation and reading documentation etc, there is one thing I don't seem to understand quite well.

Lets assume I host three web applications on my server and thus need three databases accordingly. For instance one is a webshop with product and invoice tables, one is a weblog with article and comment tables and another one is a web based game with game stats tables (simplification obviously).

So I host multiple sites on one installation of mysql, and each application I run on my server gets its own database with tables, fields and content.

Now, with CouchDb I want do the exact same thing. The problem seems to be that creating a database in CouchDb, is more similar to creating a table in mysql. I.e. I create databases called 'comments', 'articles' etc. for my weblog and inside I create a document per article or a document per comment.

So my question is: how can I separate my data from multiple web applications on one CouchDB installation?

I think I am doing something fundamentally wrong here but hopefully one of you guys can help me get on the right track.

Answer 1

@Zombies is extremely right about performance. CouchDB isn't suited to perform on a lot of documents in a single database. If you need to perform on, let's say, more than 5000 documents, MongoDB will outperfom CouchDB.

Views in CouchDB are essential, but painful, with limited JavaScript options to build your queries (don't even think about document references or nested objects). Considering having multiples databases for different documents is quite the solution. Some people will say something like:

CouchDB is a NoSQL database, and as such you should not need to order your documents nor filtering them using something else than views. NoSQL database core feature is the ability to store scheme-less documents [...]

And I find it very annoying when you need to find a workaround to performance and querying. You should not mind creating a few databases to separate your data if it allows you to split your data, it will still be on a 'single CouchDB installation'. Don't forget that CouchDB is suited for small databases. The smallest a database will be, the fastest your query will be, the better the performance will be.

(I do not know if there are any english mistakes, pardon me if so)

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EDIT Some companies like ArangoDB made a comparison between themselves, MongoDB and CouchDB, and it is confirming my saying about the number of documents. This is the result:

There are a lot of other resources on their website. On the other hand, this statement was a personnal experience, and from benchmarking them for my internship, with a .PHP benchmarking software I found on the Internet. The results are provided below:

Answer 2

From my experience with couchdb, separating unrelated data into different databases is very important for performance and also a no-brainer. The view generation is a painful part of couchdb. Everytime the database is updated, the views (think of them as indexes in a traditional relational sql db) have to be regenerated. This involves iterating every document in the database. So if you have say 2 million documents of type A, and you have 300 documents of type, B. And you need to regenerate a view the queries type B, then all 2 million and 300 hundred enumerations will be performed during view generation and it will take a long time (it might even do a read-timeout).

Therefore, having multiple databases is a no-brainer when it comes to keeping views (how you query in couchdb, an obviously important and unavoidable feature) updated.

Answer 3

In CouchDB, there's no explicit need to separate unrelated data into multiple databases. If you've constructed your documents and views correctly, only relevant data will appear in your queries.

If you do decide to separate your data into separate databases, simply create a new database.

$ curl -X PUT http://localhost:5984/somedb
{"ok":true}