> sourcedb = db.getSisterDB('sourcedb')
sourcedb
> destdb = db.getSisterDB('destdb')
destdb
> sourcedb.coll1.insert({foo: 'bar'})
> sourcedb.coll1.find()
{ "_id" : ObjectId("52ebcb2ab33a160d3f1fb6fe"), "foo" : "bar" }
> 
> 
> destdb.coll1.insert({ "_id" : ObjectId("52ebcb2ab33a160d3f1fb6fe"), "foo" : "bar2" })
> destdb.coll1.insert({"name": "Sergio"})
> 
> 
> destdb.coll1.find()
{ "_id" : ObjectId("52ebcb2ab33a160d3f1fb6fe"), "foo" : "bar2" }
{ "_id" : ObjectId("52ebcb6bb33a160d3f1fb6ff"), "name" : "Sergio" }
> 
> 
> db.copyDatabase('sourcedb', 'destdb', 'localhost:27017')
{
	"errmsg" : "exception: E11000 duplicate key error index: destdb.coll1.$_id_  dup key: { : ObjectId('52ebcb2ab33a160d3f1fb6fe') }",
	"code" : 11000,
	"ok" : 0
}
>