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https://issues.apache.org/jira/browse/HDDS-2679?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16988936#comment-16988936
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Marton Elek commented on HDDS-2679:
-----------------------------------
Discussed earlier with [~msingh] and [~arp]
> Ratis ring creation might be failed with async pipeline creation
> -----------------------------------------------------------------
>
> Key: HDDS-2679
> URL: https://issues.apache.org/jira/browse/HDDS-2679
> Project: Hadoop Distributed Data Store
> Issue Type: Improvement
> Components: Ozone Datanode, SCM
> Reporter: Marton Elek
> Priority: Blocker
>
> The problem introduced with async pipeline creation:
>
> # Let's say the SCM got registration from three datanodes.
> # A Ratis/THREE pipeline will be created on SCM
> # With the next HB Datanode1(DN1) will receive the CreatePipeline command
> # Datanode1 will start the Ratis server which tries to get votes from DN2
> and DN3
> # If DN2 has not yet received the CreatePipeline command (which has high
> chance with 30sec HB) it will refuse to vote to DN1
> # DN1 will request a pipeline close from the SCM as there are no votes from
> DN2 and DN3
> # Pipeline is closed on SCM side, but in the mean time DN2 (finally)
> receives the pipeline creation command and tries to get votes, but DN1 has a
> newer group/pipeline id.
> # And so on
> If we are lucky enough after a while all DN will receive the container
> creation at more or less the same time, but if not, SCM couldn't create an
> Open Ratis
>
> Possible solutions:
> * At the very beginning datanode can trust in the peers and learn the group
> id (but it doesn't cover the case when one pipeline has been closed on DN1
> *and* a new pipeline is created but DN2 still has the old pipeline).
> * We can use bidirectional GRPC streaming for datanode scm communication
> (which is a good idea anyway to make the communication faster). It makes the
> communication faster but the problem is still there if there is a network
> blip between scm and DN1
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