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From "Todd Lipcon (Commented) (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (HDFS-2791) If block report races with closing of file, replica is incorrectly marked corrupt
Date Tue, 24 Jan 2012 04:29:40 GMT

    [ https://issues.apache.org/jira/browse/HDFS-2791?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13191865#comment-13191865
] 

Todd Lipcon commented on HDFS-2791:
-----------------------------------

The code path calls {{markBlockAsCorrupt}} which adds it to {{corruptReplicasMap}}. This will
cause another replica to get made, and then the original will be deleted -- wasted work but
not the end of the world.

In the non-HA case, this is probably OK. But in the HA case, this race can happen even when
a file's replication count is 1, in which case it will get marked corrupt and then no new
copy can be made. The block will be corrupt until the next full block report.
                
> If block report races with closing of file, replica is incorrectly marked corrupt
> ---------------------------------------------------------------------------------
>
>                 Key: HDFS-2791
>                 URL: https://issues.apache.org/jira/browse/HDFS-2791
>             Project: Hadoop HDFS
>          Issue Type: Bug
>          Components: data-node, name-node
>    Affects Versions: 0.22.0, 0.23.0
>            Reporter: Todd Lipcon
>            Assignee: Todd Lipcon
>         Attachments: hdfs-2791-test.txt, hdfs-2791.txt, hdfs-2791.txt, hdfs-2791.txt
>
>
> The following sequence of events results in a replica mistakenly marked corrupt:
> 1. Pipeline is open with 2 replicas
> 2. DN1 generates a block report but is slow in sending to the NN (eg some flaky network).
It gets "stuck" right before the block report RPC.
> 3. Client closes the file.
> 4. DN2 is fast and sends blockReceived to the NN. NN marks the block as COMPLETE
> 5. DN1's block report proceeds, and includes the block in an RBW state.
> 6. (x) NN incorrectly marks the replica as corrupt, since it is an RBW replica on a COMPLETE
block.

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