[jira] [Commented] (HADOOP-11466) Newer Fast byte comparison is slower in SUN SPARC machines

["Colin Patrick McCabe (JIRA)" <ji...@apache.org>]

    [ https://issues.apache.org/jira/browse/HADOOP-11466?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14275724#comment-14275724 ] 

Colin Patrick McCabe commented on HADOOP-11466:
-----------------------------------------------

Thanks, Suman.  Can you add a {{LOG.trace}} in both cases so that we can turn up the log level when needed to get some logs?

> 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
>             Fix For: 3.0.0
>
>         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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