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https://issues.apache.org/jira/browse/RATIS-840?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17090357#comment-17090357
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Tsz-wo Sze edited comment on RATIS-840 at 4/23/20, 7:45 AM:
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[~yjxxtd], in this JIRA, let's focus on fixing voterLists.
For the restart problem, we may limit the number of alive GrpcLogAppenders, say
3. When creating the 4th GrpcLogAppender, it has to wait until a previous
appender dead. Sound good? We should do it in a separated JIRA.
was (Author: szetszwo):
[~yjxxtd], in this JIRA, let's focus on fixing voterLists.
For the restart problem, we may limit the number of alive GrpcLogAppender, say
3. When creating the fourth GrpcLogAppender, it has to wait unit a previous
appender dead. Sound good? We should do it in a separated JIRA.
> 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: Critical
> Attachments: RATIS-840.001.patch, RATIS-840.002.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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