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https://issues.apache.org/jira/browse/RATIS-2137?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17872761#comment-17872761
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Kevin Liu commented on RATIS-2137:
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[~szetszwo] Do you have any idea about this issue?
> Leader fails to send correct index to follower after timeout exception
> ----------------------------------------------------------------------
>
> Key: RATIS-2137
> URL: https://issues.apache.org/jira/browse/RATIS-2137
> Project: Ratis
> Issue Type: Bug
> Affects Versions: 2.5.1
> Reporter: Kevin Liu
> Priority: Major
>
> I found that after the following log, the follower became unavailable
> 24/08/11 09:03:13,714 INFO [nioEventLoopGroup-3-3] RaftServer$Division:
> 1@group-47BEDE733167: Failed appendEntries as the first entry (index
> 34795876) already exists (snapshotIndex: 34670809, commitIndex: 34795893)
> 24/08/11 09:03:13,714 INFO [nioEventLoopGroup-3-3] RaftServer$Division:
> 1@group-47BEDE733167: inconsistency entries.
> Reply:3<-1#2559343:FAIL-t59,INCONSISTENCY,nextIndex=34795894,followerCommit=34795893,matchIndex=-1
> 24/08/11 09:03:13,715 INFO [nioEventLoopGroup-3-3] RaftServer$Division:
> 1@group-47BEDE733167: Failed appendEntries as the first entry (index
> 34795875) already exists (snapshotIndex: 34670809, commitIndex: 34795893)
> 24/08/11 09:03:13,715 INFO [nioEventLoopGroup-3-3] RaftServer$Division:
> 1@group-47BEDE733167: inconsistency entries.
> Reply:3<-1#2559406:FAIL-t59,INCONSISTENCY,nextIndex=34795894,followerCommit=34795893,matchIndex=-1
> Here is what I found in the leader's log
> 24/08/11 09:03:10,130 WARN
> [3@group-47BEDE733167->1-LogAppenderDefault-LogAppenderDaemon] LogAppender:
> 3@group-47BEDE733167->1-LogAppenderDefault: Failed to appendEntries
> (retry=1): org.apache.ratis.protocol.exceptions.TimeoutIOException
> 24/08/11 09:03:13,714 INFO
> [3@group-47BEDE733167->1-LogAppenderDefault-LogAppenderDaemon] FollowerInfo:
> 3@group-47BEDE733167->1: decreaseNextIndex nextIndex: updateUnconditionally
> 34795876 -> 34795875
> 24/08/11 09:03:13,715 INFO
> [3@group-47BEDE733167->1-LogAppenderDefault-LogAppenderDaemon] FollowerInfo:
> 3@group-47BEDE733167->1: decreaseNextIndex nextIndex: updateUnconditionally
> 34795875 -> 34795874
> I guess when the leader called appendEntries for the first time, the follower
> had been executed successfully, but the leader did not receive the follower's
> response and times out. When it resent, it found that it could not match the
> change and started to decreaseNextIndex.
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