GlenGeng commented on a change in pull request #383:
URL: https://github.com/apache/incubator-ratis/pull/383#discussion_r552334420
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File path:
ratis-server/src/main/java/org/apache/ratis/server/impl/RaftServerImpl.java
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@@ -104,6 +104,20 @@ public RaftPeerRole getCurrentRole() {
return getRole().getCurrentRole();
}
+ @Override
+ public boolean isLeader() {
Review comment:
@runzhiwang Thanks for the tag. I have following suggestions:
1. I agree that leader should sort the `sendTsWithAck` increasingly, and
iterate from large to small to pick the `sendTsWithAck` that majority of the
followers(including himself) has replied the leader as the `startOfLease` .
2. We can use `LeaderStateImpl#checkLeadership` to calculate and maintain
the lease, and step down when lease is expired. `isLeader()` might be called
hundreds or thousands times per second, which would be a potential waste to
resource. `LeaderStateImpl#checkLeadership` can make leader step down if lease
is expired, which is more suitable for the semantics of lease.
3. We may not need the `LEADER_LEASE_TIMEOUT_RATIO_KEY ` at the very
beginning. What we worry about is the lease is too short to make leader
unstable, and we can revisit the `clock drift bound` feature later.
4. To maintain the lease, the follower should withhold its vote if its has
replied the AppendEntriesRequest, even it meets a RequestVoteRequest with
higher term and newer raft log. Seems the RequestVote logic is not touched in
this PR ?
5. I suggest that leader should step down when the maintained lease is
expired. From the view of App layer, `isLeaderReady()` means raft server has
become leader, yet the `appliedLogIndex` of StateMachine has not reach the
`lastLogIndex`, As soon as `isLeaderReady()` return true, the App layer would
expect leader not return false during the whole term.
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