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• The timer service keeps timers for all the keys, and it will fire timers based on the watermark.

Mixed mode:

• Before the source operator emits isBacklog=false, the timer service would fire processing-time timers based on the system time.
• At the point when isBacklog switches to false, the timer service would fire event-time timers up to the latest watermark at this point keeps timers only for the current key, and it will fire timers of the current key up to the last watermark during backlog at the end of each key. And all the processing time timer up to the current system time will be triggered.
  
  • The value of InternalTimeService#getCurrentWatermark will be Watermark.MIN_VALUE when processing a key and will be set to the last watermark during backlog when firing triggers.
• After isBacklog switches to false, the timer service keeps timers for all the keys and fires timers as the watermark advances.

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