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https://issues.apache.org/jira/browse/HIVE-12348?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
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Teddy Choi updated HIVE-12348:
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Description:
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.
> String 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
>
> 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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