关于mongodb上限集合的困惑

Question

I am new to mongodb. Here is a code snippet:

MongoClient mongo = new MongoClient("localhost", 27017);
DB db = mongo.getDB("testdb");
DBCollection collection = db.getCollection("user");

for db.getCollection("user") , if there is an existing collection named "user", it will return this collection. If "user" does not exit, getCollection("user") will create a new collection. Now I want to know what type of collection does getCollection create. Does getCollection return a capped collection?

I have read mongodb manual:

You must create capped collections explicitly using the createCollection() method.

Does this mean the collection created by getCollection is not capped collection?

Also I want to know:

1. What is the max default size for a DBcollection on 32 bit system?
2. What is the max number of collections within a db?

Answer 1

MongoDB does not create a capped collection except through the technique you describe (it could be created through an API or the shell).

Max default size for a collection? Around 2GB on a 32 bit system. However, 10gen does not recommend the 32bit build for a production system (see here).

Maximum number of collections is a bit more complex, and is best explained by the documentation .

Answer 2

Mongodb capped collection has so many restrictions, see the link http://docs.mongodb.org/manual/core/capped-collections/ . I would recommend TTL rather which helps achieve the same aim. You can find more about TTL here http://docs.mongodb.org/manual/tutorial/expire-data/ .