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Posted to common-issues@hadoop.apache.org by GitBox <gi...@apache.org> on 2020/12/18 19:43:01 UTC

[GitHub] [hadoop] NickyYe commented on pull request #2562: HDFS-15737. Don't remove datanodes from outOfServiceNodeBlocks while checking in DatanodeAdminManager

NickyYe commented on pull request #2562:
URL: https://github.com/apache/hadoop/pull/2562#issuecomment-748285060


   > ConcurrentModificationException
   
   Thanks for looking. If there are only 2 datanodes in outOfServiceNodeBlocks and the first one is removed, then it will be a dead loop on the second datanode. If there are more than 2 datanodes and the first one is removed, there will be a ConcurrentModificationException. I see both two cases in our prod very often.
   
   This issue only happens when remove (dnAdmin.stopMaintenance(dn);). By outOfServiceNodeBlocks.put(dn, blocks), it only updates the value, so Cyclic Iteration won't be affected


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