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From "Todd Lipcon (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (HDFS-4799) Corrupt replica can be prematurely removed from corruptReplicas map
Date Wed, 08 May 2013 18:29:16 GMT

    [ https://issues.apache.org/jira/browse/HDFS-4799?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13652181#comment-13652181
] 

Todd Lipcon commented on HDFS-4799:
-----------------------------------

Thanks for the review, Aaron. I'm going to leave this open for another day before committing,
just because it's an important bug and a subtle area of the code. If some of the other folks
watching this ticket want to take a look, would be very much appreciated.
                
> Corrupt replica can be prematurely removed from corruptReplicas map
> -------------------------------------------------------------------
>
>                 Key: HDFS-4799
>                 URL: https://issues.apache.org/jira/browse/HDFS-4799
>             Project: Hadoop HDFS
>          Issue Type: Bug
>          Components: namenode
>    Affects Versions: 2.0.4-alpha
>            Reporter: Todd Lipcon
>            Assignee: Todd Lipcon
>            Priority: Blocker
>         Attachments: hdfs-4799.txt, hdfs-4799-unittest.txt
>
>
> We saw the following sequence of events in a cluster result in losing the most recent
genstamp of a block:
> - client is writing to a pipeline of 3
> - the pipeline had nodes fail over some period of time, such that it left 3 old-genstamp
replicas on the original three nodes, having recruited 3 new replicas with a later genstamp.
> -- so, we have 6 total replicas in the cluster, three with old genstamps on downed nodes,
and 3 with the latest genstamp
> - cluster reboots, and the nodes with old genstamps blockReport first. The replicas are
correctly added to the corrupt replicas map since they have a too-old genstamp
> - the nodes with the new genstamp block report. When the latest one block reports, chooseExcessReplicates
is called and incorrectly decides to remove the three good replicas, leaving only the old-genstamp
replicas.

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