[GitHub] [incubator-ratis] runzhiwang opened a new pull request #64: RATIS-883. Fix Failed UT: testStateMachineMetrics.checkFollowerCommitLagsLeader

Mon, 27 Apr 2020 00:41:46 -0700 


runzhiwang opened a new pull request #64:
URL: https://github.com/apache/incubator-ratis/pull/64


   **What's the problem ?**
   
![image](https://user-images.githubusercontent.com/51938049/80346497-6db45800-889d-11ea-80c8-4ac8842f4dc0.png)
   
   **What's the reason ?**
   The reason is follower update commitInfoCache after leader.
   
   The stack of follower update commitInfoCache is: 
   RaftServerImpl::appendEntriesAsync
   -> state.updateStateMachine 
   -> StateMachineUpdater::applyLog 
   -> RaftServerImpl::applyLogToStateMachine
   -> RaftServerImpl::replyPendingRequest 
   -> RaftServerImpl::getCommitInfos 
   -> infos.add(commitInfoCache.update(getPeer(), 
state.getLog().getLastCommittedIndex())) 
   -> CommitInfoCache::update.
   
   The stack of leader update commitInfoCache is: 
   follower finish RaftServerImpl::appendEntriesAsync and return reply
   -> GrpcLogAppender::runAppenderImpl 
   -> GrpcLogAppender::appendLog 
   ->LogAppender::createRequest 
   ->LeaderState::newAppendEntriesRequestProto 
   ->RaftServerImpl::getCommitInfos 
   ->LeaderState::updateFollowerCommitInfos
   ->CommitInfoCache::update.
   
   Because follower need to notify thread StateMachineUpdater to update 
CommitInfoCache, we can not ensure follower update CommitInfoCache before 
leader.
   
   **How to fix ?**
   Follower update CommitInfoCache before return reply to leader.


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