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From "Raghu Angadi (JIRA)" <j...@apache.org>
Subject [jira] Commented: (HADOOP-4556) Block went missing
Date Fri, 31 Oct 2008 21:35:44 GMT

    [ https://issues.apache.org/jira/browse/HADOOP-4556?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12644434#action_12644434

Raghu Angadi commented on HADOOP-4556:

yes. E.g. : 

- P and Q have a block B. Say B is over replicated to R and P is asked to delete the block.

- Now Q and R have the block and there is a pending delete-request to P. 
- Now P is marked dead and P comes back up again. 
- block will become over replicated and NN asks Q to delete it.
- Now the block will be delete from both P and Q! Block is under replicated.

Does it seem right? IOW, why do we not want to remove the pending deletion requests?

The above example shows loss of one replica unintentionally. The real example is lot crazier
in terms of how the DNs were maked dead and came back alive and we ended up losing all the
replicas. I don't know yet  why the heartbeat was lost.

Note that this in no way means we should not fix HADOOP-4540. These are two different problems
(or two parts of a problem).

> Block went missing
> ------------------
>                 Key: HADOOP-4556
>                 URL: https://issues.apache.org/jira/browse/HADOOP-4556
>             Project: Hadoop Core
>          Issue Type: Bug
>          Components: dfs
>    Affects Versions: 0.17.2
>            Reporter: Robert Chansler
>            Assignee: Hairong Kuang
> Suspicion that all replicas of a block were marked for deletion. (Don't panic, investigation

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