[jira] [Commented] (HDFS-7443) Datanode upgrade to BLOCKID_BASED_LAYOUT fails if duplicate block files are present in the same volume

["Colin Patrick McCabe (JIRA)" <ji...@apache.org>]

    [ https://issues.apache.org/jira/browse/HDFS-7443?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14252373#comment-14252373 ] 

Colin Patrick McCabe commented on HDFS-7443:
--------------------------------------------

Oh yeah, and this patch changes {{hadoop-24-datanode-dir.tgz}} to have a duplicate block (present in multiple subdirectories in a volume), so that we are exercising the collision-handling pathway.

> Datanode upgrade to BLOCKID_BASED_LAYOUT fails if duplicate block files are present in the same volume
> ------------------------------------------------------------------------------------------------------
>
>                 Key: HDFS-7443
>                 URL: https://issues.apache.org/jira/browse/HDFS-7443
>             Project: Hadoop HDFS
>          Issue Type: Bug
>    Affects Versions: 2.6.0
>            Reporter: Kihwal Lee
>            Assignee: Colin Patrick McCabe
>            Priority: Blocker
>         Attachments: HDFS-7443.001.patch
>
>
> When we did an upgrade from 2.5 to 2.6 in a medium size cluster, about 4% of datanodes were not coming up.  They treid data file layout upgrade for BLOCKID_BASED_LAYOUT introduced in HDFS-6482, but failed.
> All failures were caused by {{NativeIO.link()}} throwing IOException saying {{EEXIST}}.  The data nodes didn't die right away, but the upgrade was soon retried when the block pool initialization was retried whenever {{BPServiceActor}} was registering with the namenode.  After many retries, datenodes terminated.  This would leave {{previous.tmp}} and {{current}} with no {{VERSION}} file in the block pool slice storage directory.  
> Although {{previous.tmp}} contained the old {{VERSION}} file, the content was in the new layout and the subdirs were all newly created ones.  This shouldn't have happened because the upgrade-recovery logic in {{Storage}} removes {{current}} and renames {{previous.tmp}} to {{current}} before retrying.  All successfully upgraded volumes had old state preserved in their {{previous}} directory.
> In summary there were two observed issues.
> - Upgrade failure with {{link()}} failing with {{EEXIST}}
> - {{previous.tmp}} contained not the content of original {{current}}, but half-upgraded one.
> We did not see this in smaller scale test clusters.



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