ChenSammi commented on pull request #508: URL: https://github.com/apache/ratis/pull/508#issuecomment-929960558
> Thanks @ChenSammi for the patch. This should be disabled by default in ratis as @szetszwo suggested, > > The only problem i think what we will run into eventually will be : > > If a slow follower is just not able to catch up with the leader and exceeds the threshold, the leader itself will not be able to apply the transactions whatever have already been appended to its own log . In such cases, probably, it should be able to remove the node and apply the pending transactions which have been appended on the raft log,. > If the slow follower is alive and function well, it will eventually catch up when the leader and another follower are waiting for it. If the slow follower doesn't response, it will eventually trigger the pipeline close after "raft.server.rpc.slowness.timeout" timeout(300s in Ozone). Removing a slow follwer node, leave the two members keep going on, or shall we add another new member to the raft group? > Also, a degenerate case will be where we are not updating the majority index to the max but the min of the nodes, but, the leader itself will be accepting accepting transactions till the pending request limit is reached. > > The other approach can be to not remove the entry from the cache aggressively once applyTransaction is called in Ozone. it should be available on the data cache as long as it is within the threshold of difference between majority and min index The Once it exceeds the threshold , the pipeline can be closed. The data in the stateMachine case will be there in the cache, until all the followers get the data(majority index == min index) . Once all the nodes have the data, or the gap between majority and min index is within the threshold , the entry will always be in the cache. Otherwise, remove the entry from cache and mark the node as slow follower and handle the slow follower case in ozone by closing down the pipeline. I opened a Ozone ticket for the cache improvement HDDS-5791. -- This is an automated message from the Apache Git Service. To respond to the message, please log on to GitHub and use the URL above to go to the specific comment. To unsubscribe, e-mail: [email protected] For queries about this service, please contact Infrastructure at: [email protected]
