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https://issues.apache.org/jira/browse/RATIS-1796?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17697209#comment-17697209
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Kaijie Chen commented on RATIS-1796:
------------------------------------
{quote} There is a race between leader election and committing new logs. Yes,
we can increase the term early to avoid changing back to follower by
appendEntries. However, the old leader and the other follower won't vote for it
since they have committed new log.{quote}
We have already blocked client requests during transfer leadership, so the old
leader shouldn't get new logs.
And we only send startElection to the transferee when it's up-to-date.
So the appendEntries here is actually heartbeat.
{quote}The question is – do we support transfer leadership when the group is
busy? If yes, we need to step down the leader first. We may provide an option
to "force" transfer leadership.{quote}
We don't need to step down the leader first, it will step down when the
transferee increased its term.
We just need to block client request on the old leader to make sure the log
doesn't grow anymore.
Currently, yield leadership to higher priority peer doesn't block client
request, I have some idea to change it.
When the old leader detects a peer with higher priority, it will start a
TransferLeadership (blocking) *iff* the peer is up-to-date.
> Fix TransferLeadership stopped by appendEntries from old leader
> ---------------------------------------------------------------
>
> Key: RATIS-1796
> URL: https://issues.apache.org/jira/browse/RATIS-1796
> Project: Ratis
> Issue Type: Sub-task
> Reporter: Kaijie Chen
> Assignee: Kaijie Chen
> Priority: Major
> Time Spent: 50m
> Remaining Estimate: 0h
>
> Candidate state of transferee may be stopped by the appendEntries from old
> leader, see the log below
> {code:java}
> 2023-02-28 04:52:45,026 [s0-server-thread1] INFO impl.TransferLeadership
> (TransferLeadership.java:tryTransferLeadership(107)) - s0@group-43918D205BB2:
> start transferring leadership to s1
> 2023-02-28 04:52:45,029 [s0-server-thread1] INFO impl.TransferLeadership
> (TransferLeadership.java:tryTransferLeadership(116)) - s0@group-43918D205BB2:
> sent StartLeaderElection to transferee s1 immediately as it already has
> up-to-date log
> 2023-02-28 04:52:45,031 [grpc-default-executor-6] INFO impl.RoleInfo
> (RoleInfo.java:shutdownFollowerState(111)) - s1: shutdown
> s1@group-43918D205BB2-FollowerState
> 2023-02-28 04:52:45,032 [s1@group-43918D205BB2-FollowerState] INFO
> impl.FollowerState (FollowerState.java:run(152)) -
> s1@group-43918D205BB2-FollowerState was interrupted
> 2023-02-28 04:52:45,032 [grpc-default-executor-6] INFO impl.RoleInfo
> (RoleInfo.java:updateAndGet(140)) - s1: start
> s1@group-43918D205BB2-LeaderElection4
> 2023-02-28 04:52:45,054 [s1-server-thread1] INFO impl.RoleInfo
> (RoleInfo.java:shutdownLeaderElection(131)) - s1: shutdown
> s1@group-43918D205BB2-LeaderElection4
> 2023-02-28 04:52:45,054 [s1-server-thread1] INFO impl.RoleInfo
> (RoleInfo.java:startFollowerState(104)) - s1: startFollowerState
> reason:appendEntries from s0 term 1,
> trace: java.base/java.lang.Thread.getStackTrace(Thread.java:1602),
>
> org.apache.ratis.server.impl.RoleInfo.startFollowerState(RoleInfo.java:104),
>
> org.apache.ratis.server.impl.RaftServerImpl.changeToFollower(RaftServerImpl.java:547),
>
> org.apache.ratis.server.impl.RaftServerImpl.changeToFollowerAndPersistMetadata(RaftServerImpl.java:556),
>
> org.apache.ratis.server.impl.RaftServerImpl.appendEntriesAsync(RaftServerImpl.java:1498),
>
> org.apache.ratis.server.impl.RaftServerImpl.appendEntriesAsync(RaftServerImpl.java:1396),
>
> org.apache.ratis.server.impl.RaftServerProxy.lambda$appendEntriesAsync$26(RaftServerProxy.java:639),
> org.apache.ratis.util.JavaUtils.callAsUnchecked(JavaUtils.java:117),
>
> org.apache.ratis.server.impl.RaftServerImpl.lambda$executeSubmitServerRequestAsync$11(RaftServerImpl.java:818),
>
> java.base/java.util.concurrent.CompletableFuture$AsyncSupply.run(CompletableFuture.java:1700),
>
> java.base/java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1128),
>
> java.base/java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:628),
> java.base/java.lang.Thread.run(Thread.java:829)
> 2023-02-28 04:52:45,055 [s1-server-thread1] INFO impl.RoleInfo
> (RoleInfo.java:updateAndGet(140)) - s1: start
> s1@group-43918D205BB2-FollowerState
> {code}
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