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From "dhruba borthakur (JIRA)" <j...@apache.org>
Subject [jira] Created: (HADOOP-1187) DFS Scalability: avoid scanning entire list of datanodes in getAdditionalBlocks
Date Fri, 30 Mar 2007 21:33:25 GMT
DFS Scalability: avoid scanning entire list of datanodes in getAdditionalBlocks
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                 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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