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From "Ariel Weisberg (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (CASSANDRA-13903) Add JDK9 vectorizedMismatch array compare support
Date Tue, 10 Jul 2018 21:00:00 GMT

    [ https://issues.apache.org/jira/browse/CASSANDRA-13903?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16539224#comment-16539224
] 

Ariel Weisberg commented on CASSANDRA-13903:
--------------------------------------------

I would be interested to see it performs for small and large sizes of arrays. Is there a startup
time penalty for using the intrinsic is what I am wondering?

> Add JDK9 vectorizedMismatch array compare support
> -------------------------------------------------
>
>                 Key: CASSANDRA-13903
>                 URL: https://issues.apache.org/jira/browse/CASSANDRA-13903
>             Project: Cassandra
>          Issue Type: Improvement
>          Components: Local Write-Read Paths
>            Reporter: Yingqi Lu
>            Priority: Major
>              Labels: Performance
>
> Dear All,
> JDK9 has recently been released (http://openjdk.java.net/projects/jdk9/). It introduces
a set of new vectorizedMismatch APIs for array comparison. On supported platforms, the new
JDK9 implementation is intrisified to leverage SIMD instructions. For a byte array comparison,
up to 64 bytes (512 bits) can be compared as a single unit. Feature details please refer to
http://download.java.net/java/jdk9/docs/api/java/util/Arrays.html and https://bugs.openjdk.java.net/browse/JDK-8033148
> Currently in Cassandra, keys are implemented as ByteBuffers and compared as byte arrays
most of the time. Key comparison, for example decorated key compare, it is either done with
unsafe operation taking 8 bytes at a time, or pure java operation comparing byte by byte.
This can be optimized with new JDK9 java.util.Arrays.compare APIs on modern CPUs.
> Please let us know your feedback. At the meantime, we will submit a patch with performance
studies in couple of weeks.
> Thanks,
> Yingqi Lu



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