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From "Colin Patrick McCabe (JIRA)" <j...@apache.org>
Subject [jira] [Created] (HDFS-4953) enable HDFS local reads via mmap
Date Wed, 03 Jul 2013 01:11:20 GMT
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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