[GitHub] [hadoop] virajjasani edited a comment on pull request #3280: HDFS-16171. De-flake testDecommissionStatus

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virajjasani edited a comment on pull request #3280:
URL: https://github.com/apache/hadoop/pull/3280#issuecomment-897418170


   Thanks @ferhui for the review.
   
   > This PR tile is different from HDFS-12188
   
   Updated Jira title because testDecommissionStatus test is present in both `TestDecommissioningStatus` and `TestDecommissioningStatusWithBackoffMonitor`, hence by just mentioning testDecommissionStatus, we are taking care of both tests failures.
   
   > Do you explain why test is flaky and how you fix it?
   
   The no of under-replicated blocks on DN2 can either be 3 or 4 depending on actual blocks available in Datanode Storage. Hence, in order to make sure that once both DN1 and DN2 are decommissioned -- we have 4 under replicated blocks -- we need to first wait for total 8 blocks to be reported (including replicas) by both DNs together. This is the additional check. Once we make sure of this, we won't run in flaky test failures where sometimes due to 1 replica not being reported even before we start decommissioning, we might run into case where we can't asset all 4 blocks to be under replicated.
   Hence, I have added additional validation before we start decommissioning DN1.
   
   > I see you add synchronized to some functions, Does it help to fix flaky problems?
   
   Good point, it doesn't solve flaky problem as of now. I just kept it while running 2 tests in parallel so that config setup is synchronized but now it is not required. I will remove it. Thanks


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