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From "dhruba borthakur (JIRA)" <j...@apache.org>
Subject [jira] Commented: (HADOOP-1349) Corrupted blocks get deleted but not replicated
Date Thu, 10 May 2007 23:36:15 GMT

    [ https://issues.apache.org/jira/browse/HADOOP-1349?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel#action_12494913
] 

dhruba borthakur commented on HADOOP-1349:
------------------------------------------

This is a good one! This might be one of the reasons why we sometimes see under-replicated
blocks in a cluster. When you restart the namenode, does this problem get rectified automatically?

> Corrupted blocks get deleted but not replicated
> -----------------------------------------------
>
>                 Key: HADOOP-1349
>                 URL: https://issues.apache.org/jira/browse/HADOOP-1349
>             Project: Hadoop
>          Issue Type: Bug
>          Components: dfs
>            Reporter: Hairong Kuang
>             Fix For: 0.14.0
>
>
> When I test the patch to HADOOP-1345 on a two node dfs cluster, I see that dfs correctly
delete the corrupted replica and successfully retry reading from the other correct replica,
but the block does not get replicated. The block remains with only 1 replica until the next
block report comes in.
> In my testcase, since the dfs cluster has only 2 datanodes, the target of replication
is the same as the target of block invalidation.  After poking the logs, I found out that
the namenode sent the replication request before the block invalidation request. 
> This is because the namenode does not invalidate a block well. In FSNamesystem.invalidateBlock,
it first puts the invalidate request in a queue and then immediately removes the replica from
its state, which triggers the choosing a target for the block. When requests are sent back
to the target datanode as a reply to a heartbeat message, the replication requests have higher
priority than the invalidate requests.
> This problem could be solved if a namenode removes an invalidated replica from its state
only after the invalidate request is sent to the datanode.

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