[GitHub] [flink] alpinegizmo commented on a change in pull request #8106: [FLINK-12092] [docs]Clarity when `onTimer(...)` is called

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alpinegizmo commented on a change in pull request #8106: [FLINK-12092] [docs]Clarity when `onTimer(...)` is called
URL: https://github.com/apache/flink/pull/8106#discussion_r273737265
 
 

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 File path: docs/dev/stream/operators/process_function.md
 ##########
 @@ -44,8 +44,8 @@ For fault-tolerant state, the `ProcessFunction` gives access to Flink's [keyed s
 The timers allow applications to react to changes in processing time and in [event time]({{ site.baseurl }}/dev/event_time.html).
 Every call to the function `processElement(...)` gets a `Context` object which gives access to the element's
 event time timestamp, and to the *TimerService*. The `TimerService` can be used to register callbacks for future
-event-/processing-time instants. When a timer's particular time is reached, the `onTimer(...)` method is
-called. During that call, all states are again scoped to the key with which the timer was created, allowing
+event-/processing-time instants. The `onTimer(...)` method is
+called when such an event-time is first caught up by a watermark or such a processing-time is reached. During that call, all states are again scoped to the key with which the timer was created, allowing
 
 Review comment:
   I suggest:
   
   With event-time timers, the `onTimer(...)` method is called when the current watermark is advanced up to or beyond the timestamp of the timer, while with processing-time timers, `onTimer(...)` is called when wall clock time reaches the specified time. 

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