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From "dhruba borthakur (JIRA)" <j...@apache.org>
Subject [jira] Updated: (HADOOP-1187) DFS Scalability: avoid scanning entire list of datanodes in getAdditionalBlocks
Date Mon, 02 Apr 2007 16:02:32 GMT

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

dhruba borthakur updated HADOOP-1187:
-------------------------------------

    Attachment: clientPendingCreate.patch

A reference to the client's datanode descriptor is stored in pendingCreates. This avoids a
hash-lookup in getAdditionalBlock.

> 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
>         Attachments: clientPendingCreate.patch
>
>
> 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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