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From "Allen Wittenauer (JIRA)" <j...@apache.org>
Subject [jira] [Updated] (HADOOP-11466) Newer Fast byte comparison is slower in SUN SPARC machines
Date Tue, 13 Jan 2015 19:34:36 GMT

     [ https://issues.apache.org/jira/browse/HADOOP-11466?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
]

Allen Wittenauer updated HADOOP-11466:
--------------------------------------
    Fix Version/s:     (was: 3.0.0)

> Newer Fast byte comparison is slower in SUN SPARC machines
> ----------------------------------------------------------
>
>                 Key: HADOOP-11466
>                 URL: https://issues.apache.org/jira/browse/HADOOP-11466
>             Project: Hadoop Common
>          Issue Type: Improvement
>          Components: io, performance, util
>         Environment: Linux X86 and Solaris SPARC
>            Reporter: Suman Somasundar
>            Assignee: Suman Somasundar
>            Priority: Minor
>              Labels: patch
>         Attachments: HADOOP-11466.001.patch
>
>
> One difference between Hadoop 2.x and Hadoop 1.x is a utility to compare two byte arrays
at coarser 8-byte granularity instead of at the byte-level. The discussion at HADOOP-7761
says this fast byte comparison is somewhat faster for longer arrays and somewhat slower for
smaller arrays ( AVRO-939). In order to do 8-byte reads on addresses not aligned to 8-byte
boundaries, the patch uses Unsafe.getLong. The problem is that this call is incredibly expensive
on SPARC. The reason is that the Studio compiler detects an unaligned pointer read and handles
this read in software. x86 supports unaligned reads, so there is no penalty for this call
on x86. 



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