wojiaodoubao commented on PR #943:
URL: https://github.com/apache/ratis/pull/943#issuecomment-1774307566
Hi @Brokenice0415, thanks your detailed explanation! If I understand
correctly, 'setConfiguration before staring new peers' is right for most cases.
There might be a small corner case as I'll descried below. Please help review
whether it exists, thanks. I'll try to simulate it later.
1. If a peer not in C_old is asking for votes from leader, leader will crash
the peer.
2. After we call 'setConfiguration', leader will start a new LogAppender
thread, keep call appendEntries to the new peer.
3. If the new peer gets appendEntries, it will accept the leader as its
leader.
There is a race condition between 'leader appendEntries to peer 3' and 'peer
3 asks for vote from leader'. So the corner case is:
1. Originally we have a cluster with peer 0, 1, 2. Peer 0 is leader.
4. SetConfiguration to peer 0, update conf from {0, 1, 2} to {0, 1, 2, 3}.
5. Peer 0 starts a new LogAppender thread responsible for peer 3.
6. A network partition happens.
7. Start peer 3.
8. Network partition recovers.
9. A race condition between 'leader appendEntries to peer 3' and 'peer 3
asks for vote from leader' happens. If 'asks for vote' gets first, peer 3 will
shutdown.
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