[GitHub] [ratis] szetszwo commented on a diff in pull request #807: RATIS-1762. Support transfer leadership between nodes with same priority

["szetszwo (via GitHub)" <gi...@apache.org>]

szetszwo commented on code in PR #807:
URL: https://github.com/apache/ratis/pull/807#discussion_r1092786533


##########
ratis-server/src/main/java/org/apache/ratis/server/impl/TransferLeadership.java:
##########
@@ -81,10 +83,50 @@ public String toString() {
     this.server = server;
   }
 
+  private RaftPeerId getTransferee() {
+    return Optional.ofNullable(pending.get())
+        .map(r -> r.getRequest().getNewLeader()).orElse(null);
+  }
+
   boolean isSteppingDown() {
     return pending.get() != null;
   }
 
+  void onFollowerAppendEntriesReply(FollowerInfo follower) {
+    final RaftPeerId transferee = getTransferee();
+    // If TransferLeadership is in progress, and the transferee has just append some entries
+    if (follower.getPeer().getId().equals(transferee)) {
+      // If the transferee is up-to-date, send StartLeaderElection to it
+      server.getRole().getLeaderState().ifPresent(leaderState -> {

Review Comment:
   Pass `LeaderStateImple` as a parameter.  Then, we don't have to get it here.



##########
ratis-server/src/main/java/org/apache/ratis/server/impl/TransferLeadership.java:
##########
@@ -81,10 +83,50 @@ public String toString() {
     this.server = server;
   }
 
+  private RaftPeerId getTransferee() {
+    return Optional.ofNullable(pending.get())
+        .map(r -> r.getRequest().getNewLeader()).orElse(null);
+  }
+
   boolean isSteppingDown() {
     return pending.get() != null;
   }
 
+  void onFollowerAppendEntriesReply(FollowerInfo follower) {
+    final RaftPeerId transferee = getTransferee();
+    // If TransferLeadership is in progress, and the transferee has just append some entries
+    if (follower.getPeer().getId().equals(transferee)) {
+      // If the transferee is up-to-date, send StartLeaderElection to it
+      server.getRole().getLeaderState().ifPresent(leaderState -> {
+        if (leaderState.sendStartLeaderElection(follower)) {
+          LOG.info("{}: sent StartLeaderElection to transferee {} after received AppendEntriesResponse",
+              server.getMemberId(), transferee);
+        }
+      });
+    }
+  }
+
+  private void tryTransferLeadership(RaftPeerId transferee) {
+    server.getRole().getLeaderState().ifPresent(leaderState -> {

Review Comment:
   We should also pass `leaderState` as a parameter here.



##########
ratis-server/src/main/java/org/apache/ratis/server/impl/LeaderStateImpl.java:
##########
@@ -778,6 +778,7 @@ public void onFollowerSuccessAppendEntries(FollowerInfo follower) {
     } else {
       eventQueue.submit(checkStagingEvent);
     }
+    server.getTransferLeadership().onFollowerAppendEntriesReply(follower);

Review Comment:
   I wonder if we can "remember" the transferee follower so that we don't have to call it for all the other followers.



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