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https://issues.apache.org/jira/browse/RATIS-840?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
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Marton Elek updated RATIS-840:
------------------------------
    Priority: Blocker  (was: Critical)

> Memory leak of LogAppender
> --------------------------
>
>                 Key: RATIS-840
>                 URL: https://issues.apache.org/jira/browse/RATIS-840
>             Project: Ratis
>          Issue Type: Bug
>          Components: server
>            Reporter: runzhiwang
>            Assignee: runzhiwang
>            Priority: Blocker
>         Attachments: RATIS-840.001.patch, RATIS-840.002.patch, 
> RATIS-840.003.patch, image-2020-04-06-14-27-28-485.png, 
> image-2020-04-06-14-27-39-582.png, screenshot-1.png, screenshot-2.png
>
>
> *What's the problem ?*
>  When run hadoop-ozone for 4 days, datanode memory leak.  When dump heap, I 
> found there are 460710 instances of GrpcLogAppender. But there are only 6 
> instances of SenderList, and each SenderList contains 1-2 instance of 
> GrpcLogAppender. And there are a lot of logs related to 
> [LeaderState::restartSender|https://github.com/apache/incubator-ratis/blob/master/ratis-server/src/main/java/org/apache/ratis/server/impl/LeaderState.java#L428].
>  {code:java}INFO impl.RaftServerImpl: 
> 1665f5ea-ab17-4a0e-af6d-6958efd322fa@group-F64B465F37B5-LeaderState: 
> Restarting GrpcLogAppender for 
> 1665f5ea-ab17-4a0e-af6d-6958efd322fa@group-F64B465F37B5-\u003e229cbcc1-a3b2-4383-9c0d-c0f4c28c3d4a\n","stream":"stderr","time":"2020-04-06T03:59:53.37892512Z"}{code}
>  
>  So there are a lot of GrpcLogAppender did not stop the Daemon Thread when 
> removed from senders. 
>  !image-2020-04-06-14-27-28-485.png! 
>  !image-2020-04-06-14-27-39-582.png! 
>  
> *Why 
> [LeaderState::restartSender|https://github.com/apache/incubator-ratis/blob/master/ratis-server/src/main/java/org/apache/ratis/server/impl/LeaderState.java#L428]
>  so many times ?*
> 1. As the image shows, when remove group, SegmentedRaftLog will close, then 
> GrpcLogAppender throw exception when find the SegmentedRaftLog was closed. 
> Then GrpcLogAppender will be 
> [restarted|https://github.com/apache/incubator-ratis/blob/master/ratis-server/src/main/java/org/apache/ratis/server/impl/LogAppender.java#L94],
>  and the new GrpcLogAppender throw exception again when find the 
> SegmentedRaftLog was closed, then GrpcLogAppender will be restarted again ... 
> . It results in an infinite restart of GrpcLogAppender.
> 2. Actually, when remove group, GrpcLogAppender will be stoped: 
> RaftServerImpl::shutdown -> 
> [RoleInfo::shutdownLeaderState|https://github.com/apache/incubator-ratis/blob/master/ratis-server/src/main/java/org/apache/ratis/server/impl/RaftServerImpl.java#L266]
>  -> LeaderState::stop -> LogAppender::stopAppender, then SegmentedRaftLog 
> will be closed:  RaftServerImpl::shutdown -> 
> [ServerState:close|https://github.com/apache/incubator-ratis/blob/master/ratis-server/src/main/java/org/apache/ratis/server/impl/RaftServerImpl.java#L271]
>  ... . Though RoleInfo::shutdownLeaderState called before ServerState:close, 
> but the GrpcLogAppender was stopped asynchronously. So infinite restart of 
> GrpcLogAppender happens, when GrpcLogAppender stop after SegmentedRaftLog 
> close.
>  !screenshot-1.png! 
> *Why GrpcLogAppender did not stop the Daemon Thread when removed from senders 
> ?*
>  I find a lot of GrpcLogAppender blocked inside logs4j. I think it's 
> GrpcLogAppender restart too fast, then blocked in logs4j.
>  !screenshot-2.png! 
> *Can the new GrpcLogAppender work normally ?*
> 1. Even though without the above problem, the new created GrpcLogAppender 
> still can not work normally. 
> 2. When creat a new GrpcLogAppender, a new FollowerInfo will also be created: 
> LeaderState::addAndStartSenders -> 
> LeaderState::addSenders->RaftServerImpl::newLogAppender -> [new 
> FollowerInfo|https://github.com/apache/incubator-ratis/blob/master/ratis-server/src/main/java/org/apache/ratis/server/impl/RaftServerImpl.java#L129]
> 3. When the new created GrpcLogAppender append entry to follower, then the 
> follower response SUCCESS.
> 4. Then LeaderState::updateCommit -> [LeaderState::getMajorityMin | 
> https://github.com/apache/incubator-ratis/blob/master/ratis-server/src/main/java/org/apache/ratis/server/impl/LeaderState.java#L599]
>  -> 
> [voterLists.get(0) | 
> https://github.com/apache/incubator-ratis/blob/master/ratis-server/src/main/java/org/apache/ratis/server/impl/LeaderState.java#L607].
>  {color:#DE350B}Error happens because voterLists.get(0) return the 
> FollowerInfo of the old GrpcLogAppender, not the FollowerInfo of the new 
> GrpcLogAppender. {color}
> 5. Because the majority commit got from the FollowerInfo of the old 
> GrpcLogAppender never changes. So even though follower has append entry 
> successfully, the leader can not update commit. So the new created 
> GrpcLogAppender can never work normally.
> 6. The reason of unit test of runTestRestartLogAppender can pass is that it 
> did not stop the old GrpcLogAppender, and  the old GrpcLogAppender append 
> entry to follower, not the new GrpcLogAppender. If stop the old 
> GrpcLogAppender, runTestRestartLogAppender will fail.



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