[GitHub] [ratis] szetszwo commented on a diff in pull request #914: RATIS-1883. Next Index should be always larger than Match Index in Gr…

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

szetszwo commented on code in PR #914:
URL: https://github.com/apache/ratis/pull/914#discussion_r1316078058


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ratis-grpc/src/main/java/org/apache/ratis/grpc/server/GrpcLogAppender.java:
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@@ -433,7 +434,7 @@ private void onNextImpl(AppendEntriesReplyProto reply) {
         case INCONSISTENCY:
           grpcServerMetrics.onRequestInconsistency(getFollowerId().toString());
           LOG.warn("{}: received {} reply with nextIndex {}", this, reply.getResult(), reply.getNextIndex());
-          updateNextIndex(reply.getNextIndex());
+          updateNextIndex(Math.max(getFollower().getMatchIndex() + 1, reply.getNextIndex()));

Review Comment:
   > ... clears the logs and meta conf, ...
   
   The follower cannot clear the existing log.  Otherwise, the committed entries can be removed.  As an example, see the description of RATIS-1677.   BTW, `runTestBootstrapReconf` is starting new peers but not removing existing logs.
   
   > ... Match index in FollowerInfoImpl is only allowed to be changed monotonously.  ...
   
   Once the log entries are matched, it cannot be changed to unmatched later on.  This is an assumption of the Raft algorithm.



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