[jira] [Commented] (HDFS-3797) QJM: add segment txid as a parameter to journal() RPC

["Aaron T. Myers (JIRA)" <ji...@apache.org>]

    [ https://issues.apache.org/jira/browse/HDFS-3797?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13434626#comment-13434626 ] 

Aaron T. Myers commented on HDFS-3797:
--------------------------------------

Patch looks pretty good to me. One question: have you considered adding a test case that ensures that a JN which experiences this scenario will return to participating in the quorum after the next finalize/new segment?

Nit: looks like the method comment for testMissFinalizeAndNextStart got messed up a little bit: "+   *    */"
                
> QJM: add segment txid as a parameter to journal() RPC
> -----------------------------------------------------
>
>                 Key: HDFS-3797
>                 URL: https://issues.apache.org/jira/browse/HDFS-3797
>             Project: Hadoop HDFS
>          Issue Type: Sub-task
>          Components: ha
>    Affects Versions: QuorumJournalManager (HDFS-3077)
>            Reporter: Todd Lipcon
>            Assignee: Todd Lipcon
>            Priority: Minor
>         Attachments: hdfs-3797.txt
>
>
> During fault testing of QJM, I saw the following issue:
> 1) NN sends txn 5 to JN
> 2) NN gets partitioned from JN while JN remains up. The next two RPCs are missed while the partition has happened:
> 2a) finalizeSegment(1-5)
> 2b) startSegment(6)
> 3) NN sends txn 6 to JN
> This caused one of the JNs to end up with a segment 1-10 while the others had two segments; 1-5 and 6-10. This broke some invariants of the QJM protocol and prevented the recovery protocol from running properly.
> This can be addressed on the client side by HDFS-3726, which would cause the NN to not send the RPC in #3. But it makes sense to also add an extra safety check here on the server side: with every journal() call, we can send the segment's txid. Then if the JN and the client get "out of sync", the JN can reject the RPCs.

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