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Date: Wed, 3 Jul 2013 01:11:20 +0000 (UTC)
From: "Colin Patrick McCabe (JIRA)" <jira@apache.org>
To: hdfs-dev@hadoop.apache.org
Message-ID: <JIRA.12655953.1372813800093.202634.1372813880887@arcas>
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Subject: [jira] [Created] (HDFS-4953) enable HDFS local reads via mmap
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Colin Patrick McCabe created HDFS-4953:
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             Summary: enable HDFS local reads via mmap
                 Key: HDFS-4953
                 URL: https://issues.apache.org/jira/browse/HDFS-4953
             Project: Hadoop HDFS
          Issue Type: New Feature
    Affects Versions: 2.2.0
            Reporter: Colin Patrick McCabe
            Assignee: Colin Patrick McCabe


Currently, the short-circuit local read pathway allows HDFS clients to access files directly without going through the DataNode.  However, all of these reads involve a copy at the operating system level, since they rely on the read() / pread() / etc family of kernel interfaces.

We would like to enable HDFS to read local files via mmap.  This would enable truly zero-copy reads.

In the initial implementation, zero-copy reads will only be performed when checksums were disabled.  Later, we can use the DataNode's cache awareness to only perform zero-copy reads when we know that checksum has already been verified.

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