[GitHub] [helix] pkuwm commented on a change in pull request #1650: Improve auto enter maintenance mode

[GitBox <gi...@apache.org>]

pkuwm commented on a change in pull request #1650:
URL: https://github.com/apache/helix/pull/1650#discussion_r577940270



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File path: helix-core/src/main/java/org/apache/helix/controller/stages/BestPossibleStateCalcStage.java
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@@ -193,15 +193,19 @@ public Object call() {
   }
 
   // Check whether the offline/disabled instance count in the cluster reaches the set limit,
-  // if yes, pause the rebalancer, and throw exception to terminate rebalance cycle.
+  // if yes, auto enable maintenance mode, and use the maintenance rebalancer for this pipeline.
   private boolean validateOfflineInstancesLimit(final ResourceControllerDataProvider cache,
       final HelixManager manager) {
     int maxOfflineInstancesAllowed = cache.getClusterConfig().getMaxOfflineInstancesAllowed();
     if (maxOfflineInstancesAllowed >= 0) {
       int offlineCount = cache.getAllInstances().size() - cache.getEnabledLiveInstances().size();
       if (offlineCount > maxOfflineInstancesAllowed) {
+        // Enable maintenance mode in cache so the maintenance rebalancer is used for this pipeline
+        cache.enableMaintenanceMode();

Review comment:
       It's something I also thought about. It doesn't seem too much different. If ZK update fails, a `HelixException` will be thrown and the pipeline will be terminated. Either before or after ZK update is fine. The reason I put it before is I thought the logic looks a bit more clear to me, as it enables M mode immediately right after the offline count > threshold. It does not depend on helix manager is set or not.
   
   Synced with @jiajunwang offline. He also agreed either one will work. Thanks, @jiajunwang, for the review!




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