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https://issues.apache.org/jira/browse/HADOOP-1448?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel#action_12511298
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dhruba borthakur commented on HADOOP-1448:
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+1. Code looks good. One minor comment: can we enhance the unit test to test
the case that a "random" node is returned when there are no local rack or local
node available? Maybe we can invoke pseudoSortByDistance multiple times and
verify that at least some invocations return different nodes as the first entry
in the list.
> Setting the replication factor of a file too high causes namenode cpu overload
> ------------------------------------------------------------------------------
>
> Key: HADOOP-1448
> URL: https://issues.apache.org/jira/browse/HADOOP-1448
> Project: Hadoop
> Issue Type: Bug
> Components: dfs
> Affects Versions: 0.13.0
> Reporter: dhruba borthakur
> Assignee: Hairong Kuang
> Fix For: 0.14.0
>
> Attachments: getBlockLocation.patch
>
>
> The replication factor of a file in set to 300 (on a 800 node cluster). Then
> all mappers try to open this file. For every open call that the namenode
> receives from each of these 800 clients, it sorts all the replicas of the
> block(s) based on the distance from the client. This causes CPU usage
> overload on the namenode.
> One proposal is to make the namenode return a non-sorted list of datanodes to
> the client. Information about each replica also contains the rack on which
> that replica resides. The client can look at the replicas to determine if
> there is a copy on the local node. If not, then it can find out if there is a
> replica on the local rack. If not then it can choose a replica at random.
> This proposal is scalable because the sorting and selection of replicas is
> done by the client rather than the Namenode.
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