Fix Ticker

Pls check the following. If they are valid concern, pls fix them in 4.5.1

1) I see there are a few places where time.Tick() is called. time.Tick() can leak memory, but probably slowly, since it may only leak when pipeline restarts.
2) In checkpoint manager, I see a few places where new Ticker. Just to make sure Stop() is called when the Ticker is called after it is finished.