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Subject [GitHub] twalthr commented on a change in pull request #6504: [FLINK-10068][docs] Add documentation for RocksDB-based timers and st…
Date Thu, 09 Aug 2018 14:38:28 GMT
twalthr commented on a change in pull request #6504: [FLINK-10068][docs] Add documentation
for RocksDB-based timers and st…
URL: https://github.com/apache/flink/pull/6504#discussion_r208950079
 
 

 ##########
 File path: docs/dev/stream/operators/process_function.md
 ##########
 @@ -277,19 +277,18 @@ Both types of timers (processing-time and event-time) are internally
maintained
 
 The `TimerService` deduplicates timers per key and timestamp, i.e., there is at most one
timer per key and timestamp. If multiple timers are registered for the same timestamp, the
`onTimer()` method will be called just once.
 
-**Note:** Flink synchronizes invocations of `onTimer()` and `processElement()`. Hence, users
do not have to worry about concurrent modification of state.
+<span class="label label-info">Note</span> Flink synchronizes invocations of
`onTimer()` and `processElement()`. Hence, users do not have to worry about concurrent modification
of state.
 
 ### Fault Tolerance
 
 Timers are fault tolerant and checkpointed along with the state of the application. 
 In case of a failure recovery or when starting an application from a savepoint, the timers
are restored.
 
-**Note:** Checkpointed processing-time timers that were supposed to fire before their restoration,
will fire immediately. 
+<span class="label label-info">Note</span> Checkpointed processing-time timers
that were supposed to fire before their restoration, will fire immediately.
 This might happen when an application recovers from a failure or when it is started from
a savepoint.
 
-**Note:** Timers are always synchronously checkpointed, regardless of the configuration of
the state backends. 
-Therefore, a large number of timers can significantly increase checkpointing time. 
-See the "Timer Coalescing" section for advice on how to reduce the number of timers.
+<span class="label label-info">Note</span> Timers are always asynchronously checkpointed,
except for the combination of RocksDB backend / with incremental snapshots / with heap-based
timers (will be resolved with `FLINK-10026`).
 
 Review comment:
   It would be great if you could add more internal knowledge if there is more to say. This
section is very tiny but I guess a lot of work went it to so we should document it accordingly.

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