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From "dhruba borthakur (JIRA)" <j...@apache.org>
Subject [jira] Commented: (HADOOP-1187) DFS Scalability: avoid scanning entire list of datanodes in getAdditionalBlocks
Date Fri, 30 Mar 2007 23:30:25 GMT

    [ https://issues.apache.org/jira/browse/HADOOP-1187?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel#action_12485679
] 

dhruba borthakur commented on HADOOP-1187:
------------------------------------------

It could help. But if we store it in the pendingCreates, then we avoid this lookup completely.



> DFS Scalability: avoid scanning entire list of datanodes in getAdditionalBlocks
> -------------------------------------------------------------------------------
>
>                 Key: HADOOP-1187
>                 URL: https://issues.apache.org/jira/browse/HADOOP-1187
>             Project: Hadoop
>          Issue Type: Bug
>          Components: dfs
>            Reporter: dhruba borthakur
>         Assigned To: dhruba borthakur
>
> A new block allocations for a file scans the list of all known datanodes to find if the
client that is a also a cluster node. If so, then it tries to allocate a replica locally.
This check consumes plenty of CPU, especially if the number of datanodes in a cluster is large.
> An optimization: if the client is also a cluster node, then cache a reference to the
corresponding DatanodeDescriptor from the entry in pendingCreate. The method getAdditionalBlock()
uses the cached DatanodeDescriptor and thus avoids scanning the entire list of datanodes.

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