Duh. Then the trick is not to pause at all. Make sure that pause_at_recovery_target is not set in recovery.conf. Stop the recovering server, then start it again. That should do the trick.
I've tried set pause_at_recovery_target to true, it's not work. and also tried comment out this setting it's the same.
Restart have no effect, the recovery.conf is always there, I think it's should be rename to recovery.done if it's work.