[GitHub] [kafka] guozhangwang commented on a change in pull request #9531: KAFKA-10661; Add new resigned state for graceful shutdown/initialization

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guozhangwang commented on a change in pull request #9531:
URL: https://github.com/apache/kafka/pull/9531#discussion_r519551394



##########
File path: raft/src/main/java/org/apache/kafka/raft/QuorumState.java
##########
@@ -21,18 +21,21 @@
 import org.slf4j.Logger;
 
 import java.io.IOException;
+import java.util.Collections;
 import java.util.HashSet;
+import java.util.List;
 import java.util.Optional;
 import java.util.OptionalInt;
 import java.util.Random;
 import java.util.Set;
 import java.util.stream.Collectors;
 
 /**
- * This class is responsible for managing the current state of this node and ensuring only
- * valid state transitions.
+ * This class is responsible for managing the current state of this node and ensuring
+ * only valid state transitions. Below we define the possible state transitions and
+ * how they are triggered:
  *
- * Unattached =>
+ * Unattached|Resigned =>

Review comment:
       Makes me thinking: if we have an even number sized quorum (say 2N), and the leader is resigning. Then before the leader shutdown we need N+1 votes, while after the leader shutdown, the quorum size shrink to 2N-1 and we would only need N votes. So if the resigning leader gives it a vote to a candidate and then shutdown, while the candidates thinks they only need N votes, would that potentially result in two candidates claiming victory --- somehow this sounds quite close to the real world :P --- each with N votes while one of them has the vote from the resigned leader?

##########
File path: raft/src/main/java/org/apache/kafka/raft/KafkaRaftClient.java
##########
@@ -1601,7 +1618,12 @@ private long pollFollower(long currentTimeMs) throws IOException {
     }
 
     private long pollFollowerAsVoter(FollowerState state, long currentTimeMs) throws IOException {
-        if (state.hasFetchTimeoutExpired(currentTimeMs)) {
+        GracefulShutdown shutdown = this.shutdown.get();
+        if (shutdown != null) {
+            // If we are a follower, then we can shutdown immediately. We want to
+            // skip the transition to candidate in any case.
+            return 0;

Review comment:
       Why the behavior of `pollFollowerAsVoter` and `pollVoted` are different when shutting down? Could the former case still help in casting and completing a vote as well?




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