Github user fhueske commented on a diff in the pull request:
https://github.com/apache/flink/pull/5887#discussion_r183708069
--- Diff: docs/dev/stream/operators/process_function.md ---
@@ -322,3 +322,26 @@ ctx.timerService.registerEventTimeTimer(coalescedTime)
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+
+### Fault Tolerance
+
+Timers registered within `ProcessFunction` are fault tolerant.
+
+Timers registered within `ProcessFunction` will be checkpointed by Flink.
Upon restoring, timers that are checkpointed
+from the previous job will be restored on whatever new instance is
responsible for that key.
--- End diff --
Add a note that timers are synchronously checkpointed (regardless of the
configuration of the state backend). Hence, a large number of timers can
significantly increase checkpointing time. See optimizations section for advice
to reduce the number of timers.
---
