[GitHub] [ozone] GlenGeng commented on a change in pull request #2184: HDDS-5148. Bump ratis version to 2.1.0-ff8aa66-SNAPSHOT

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

GlenGeng commented on a change in pull request #2184:
URL: https://github.com/apache/ozone/pull/2184#discussion_r621131003



##########
File path: hadoop-hdds/server-scm/src/main/java/org/apache/hadoop/hdds/scm/ha/SCMStateMachine.java
##########
@@ -294,6 +294,14 @@ public void pause() {
     getLifeCycle().transition(LifeCycle.State.PAUSED);
   }
 
+  @Override
+  public void reinitialize() {
+    if (getLifeCycleState() == LifeCycle.State.PAUSED) {

Review comment:
       After `notifyInstallSnapshotFromLeader` is called, ratis calls 
   ```
                   if (reply != null) {
                     LOG.info("{}: StateMachine successfully installed snapshot index {}. Reloading the StateMachine.",
                         getMemberId(), reply.getIndex());
                     stateMachine.pause();
                     state.updateInstalledSnapshotIndex(reply);
                     state.reloadStateMachine(reply.getIndex());
                   }
   ```
   `stateMachine.pause();` will make SM to be in PAUSED state, `state.reloadStateMachine(reply.getIndex())` will trigger `StateMachineUpdater#reload()` to be called, which will then call `stateMachine.reinitialize();`.
   
   This is the reason of the fix.
   
   As far as I known,  at the end of `TestSCMInstallSnapshotWithHA#testInstallSnapshot`, the followerSCM is also in PAUSED state, which is not checked before.
   
   And for `testInstallOldCheckpointFailure`, `notifyInstallSnapshotFromLeader` is not really called, since without the fix in RATIS-1369, downloading snapshot taken at index 0 is ignore by follower SCM.




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