[GitHub] [helix] dasahcc commented on a change in pull request #1066: [WIP] Prevent parallel controller pipelines run causing two master replicas

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

dasahcc commented on a change in pull request #1066:
URL: https://github.com/apache/helix/pull/1066#discussion_r436170779



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File path: helix-core/src/main/java/org/apache/helix/controller/stages/MessageDispatchStage.java
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@@ -78,7 +78,13 @@ protected void processEvent(ClusterEvent event, MessageOutput messageOutput) thr
         batchMessage(dataAccessor.keyBuilder(), messagesToSend, resourceMap, liveInstanceMap,
             manager.getProperties());
 
-    List<Message> messagesSent = sendMessages(dataAccessor, outputMessages);
+    String expectedSession = event.getAttribute(AttributeName.CONTROLLER_LEADER_SESSION.name());
+    // An early check for expected leader session. If the sessions don't match, it means the
+    // controller lost leadership, then messages should not be sent. This potentially avoid
+    // double masters for a single partition.
+    List<Message> messagesSent = manager.getSessionId().equals(expectedSession)

Review comment:
       Shall we throw an exception to break the pipeline? If we know session is not matched. Then there is no reason to keep following pipeline based on stale data.




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