为什么mongodb oplog总是为空？

Question

I'm trying to write synchronizer between MongoDB and Lucene. Idea is to implement application that will tail oplog and reproduce everything in Lucene. As a basis I'm using this post

The problem is that my oplog is always empty:

rs0:PRIMARY> db.oplog.rs.find({},{"ts":1}).sort({$natural: -1}).hasNext()
false

rs0:PRIMARY> db.Message.find({}).count()
729

rs0:PRIMARY> db.oplog.rs.find({}).hasNext()
false

rs0:PRIMARY> db.oplog.rs.find()
rs0:PRIMARY> 

Can someone explain me what I'm doing wrong?

Answer 1

All replica set members contain a copy of the oplog, in the local.oplog.rs collection. In order to query the oplog you have to use the local database .

use local;
db.oplog.rs.find();