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Date: Thu, 7 Oct 2010 18:41:32 -0400 (EDT)
From: "Matt Foley (JIRA)" <jira@apache.org>
To: hdfs-dev@hadoop.apache.org
Subject: [jira] Created: (HDFS-1446) Refactor the start-time Directory Tree
 and Replicas Map constructors to share data and run volume-parallel
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Refactor the start-time Directory Tree and Replicas Map constructors to share data and run volume-parallel
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                 Key: HDFS-1446
                 URL: https://issues.apache.org/jira/browse/HDFS-1446
             Project: Hadoop HDFS
          Issue Type: Sub-task
          Components: data-node
    Affects Versions: 0.20.2
            Reporter: Matt Foley
            Assignee: Matt Foley
             Fix For: 0.22.0


Refactor the FSDir() and getVolumeMap() call chains in FSDataset, so they share data and run volume-parallel. Currently the two constructors for in-memory directory tree and replicas map run THREE full scans of the entire disk - once in FSDir(), once in recoverTempUnlinkedBlock(), and once in addToReplicasMap(). During each scan, a new File object is created for each of the 100,000 or so items in the native file system (for a 50,000-block node). This impacts GC as well as disk traffic.

This work item is one of four sub-tasks for HDFS-1443, Improve Datanode startup time.

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