use test2
db.test.ensureIndex(

{createdAt:1}

,

{expireAfterSeconds:1}

)
db.test.insert(

{createdAt:new Date()}

)
db.test.insert(

{createdAt:new Date()}

)
db.test.insert(

{createdAt:new Date()}

)

I keep seeing them in the collection even after 5 seconds and then suddenly all gone. I don't know if this is expected behavior or if the expireAfterSeconds is supposed to be a hard limit.