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From "Hudson (JIRA)" <j...@apache.org>
Subject [jira] Commented: (HADOOP-4643) NameNode should exclude excessive replicas when counting live replicas for a block
Date Fri, 14 Nov 2008 18:33:44 GMT

    [ https://issues.apache.org/jira/browse/HADOOP-4643?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12647691#action_12647691
] 

Hudson commented on HADOOP-4643:
--------------------------------

Integrated in Hadoop-trunk #661 (See [http://hudson.zones.apache.org/hudson/job/Hadoop-trunk/661/])
    . NameNode should exclude excessive replicas when counting live replicas for a block.
Contributed by Hairong Kuang.


> NameNode should exclude excessive replicas when counting live replicas for a block
> ----------------------------------------------------------------------------------
>
>                 Key: HADOOP-4643
>                 URL: https://issues.apache.org/jira/browse/HADOOP-4643
>             Project: Hadoop Core
>          Issue Type: Bug
>          Components: dfs
>            Reporter: Hairong Kuang
>            Assignee: Hairong Kuang
>             Fix For: 0.18.3
>
>         Attachments: nodeCount-br18.patch, nodeCount.patch
>
>
> Currently NameNode include excessive replicas in blockMap and count them as live replicas.
Although excessive replicas have marked as invalid, scheduling deletion may be delayed and
also datanode does not send deletion confirmation until the next block report. As a result,
excessive replicas may stay in blocksMap for quite a while. This may cause underReplicated
blocks undetected in NameNode. 
> For example, assume that block b is at datanode d1, d2, and d3. We have the following
scenario
> 1. d1 loses heartbeat, NN will replicate b to another datanode, assuming it is d4. 
> 2. d1 comes back. NN finds out b is over-replicated therefore choosing one replica, assuming
d4, as a excessive replica and marking it as invalid. Now b has 3 valid replicas d1, d2, d3
and 1 excessive (invalid) replica d4, all in blocksMap.
> 3. d2 loses heartbeat. d2 gets removed from blocksMap. Block b has 2 valid replicas d1
and d3, and 1 excessive invalid replica d4. Block b is under-replicated; But NN still counts
block b has 3 live replicas so does not take any action to replicate block b.

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