jiajunwang commented on a change in pull request #690: Reset the WAGED
rebalancer once the controller newly acquires leadership.
URL: https://github.com/apache/helix/pull/690#discussion_r369870892
##########
File path:
helix-core/src/main/java/org/apache/helix/controller/GenericHelixController.java
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@@ -626,6 +631,22 @@ private void handleEvent(ClusterEvent event,
BaseControllerDataProvider dataProv
return;
}
+ // Event handling happens in a different thread from the
onControllerChange processing thread.
+ // Thus, there are several possible conditions.
+ // 1. Event handled after leadership acquired. So we will have a valid
rebalancer for the
+ // event processing.
+ // 2. Event handled shortly after leadership relinquished. And the
rebalancer has not been
+ // marked as invalid yet. So the event will be processed the same as case
one.
+ // 3. Event is leftover from the previous session, and it is handled when
the controller
Review comment:
We should, but there is no good way to do it for now. And even we discard
the queued events, the concerning one is actually the one that is being
processed. Force canceling that could be risky. So I don't think to do it
without deeply improve the pipeline logic is a good idea.
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