narendly 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_r369864578
 
 

 ##########
 File path: 
helix-core/src/main/java/org/apache/helix/controller/GenericHelixController.java
 ##########
 @@ -187,6 +187,11 @@
 
   private HelixManager _helixManager;
 
+  // Since the WAGED rebalancer needs to be lazily constructed, the 
GenericHelixController will not
+  // be constructed with a WAGED rebalancer. This wrapper is to avoid the 
complexity of handling a
+  // nullable value in the GenericHelixController logic.
+  private final WagedRebalancerRef _wagedRebalancerRef = new 
WagedRebalancerRef();
 
 Review comment:
   Design suggestion:
   
   Could we make this generic by using `RebalancerRef` or 
`StatefulRebalancerRef` (since this is only a problem for stateful 
rebalancers)? Also, instead of directly instantiating, we could make this a 
cluster config and have it be dynamically created? (Waged, CrushED, etc.). That 
way, we decouple GenericHelixController from WAGED (or a particular rebalancer) 
as much as possible.
   
   It would be okay to set the default type to be WAGED since this is the only 
stateful rebalancer we have available so far?

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