[jira] [Commented] (HIVE-12348) Byte array comparison optimization for SIMD

["Ashutosh Chauhan (JIRA)" <ji...@apache.org>]

    [ https://issues.apache.org/jira/browse/HIVE-12348?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15233817#comment-15233817 ] 

Ashutosh Chauhan commented on HIVE-12348:
-----------------------------------------

[~chengxiang li] Would you like to take a look at this one?

> Byte array comparison optimization for SIMD
> -------------------------------------------
>
>                 Key: HIVE-12348
>                 URL: https://issues.apache.org/jira/browse/HIVE-12348
>             Project: Hive
>          Issue Type: Sub-task
>            Reporter: Teddy Choi
>            Assignee: Teddy Choi
>            Priority: Minor
>         Attachments: HIVE-12348.patch
>
>
> The current byte comparison implementation in Hive is basic. It handles a byte (1 byte) at a time, so it's slow.
> There's FastByteComparisons class in Hadoop with sun.misc.Unsafe class. (https://github.com/hanborq/hadoop/blob/master/src/core/org/apache/hadoop/io/FastByteComparisons.java) It handles a long integer (8 bytes) at a time, so it's faster.
> Java 8 has String.compare, String.equalTo intrinsics with AVX2 and SSE4.2. (http://hg.openjdk.java.net/jdk8/jdk8/hotspot/rev/038dd2875b94) It handles 128~256 bits (16~32 bytes) at a time, so it's much faster.
> However, Unsafe.getLong and String.compare intrinsic needs additional data copies, so the actual performance increase is smaller than "1 byte : 32 bytes" comparison.



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