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https://issues.apache.org/jira/browse/HIVE-18487?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16331283#comment-16331283
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Gopal V commented on HIVE-18487:
--------------------------------
Specific corner-case is that the _ wildcard can represent anywhere between 1-6
bytes in UTF-8.
> Vectorization: Undecoded utf-8 fast-path for _ wildcards in LIKE
> ----------------------------------------------------------------
>
> Key: HIVE-18487
> URL: https://issues.apache.org/jira/browse/HIVE-18487
> Project: Hive
> Issue Type: Improvement
> Affects Versions: 3.0.0
> Reporter: Gopal V
> Priority: Major
>
> Queries with "%" are optimized using the BoyerMooreHorspool lookups, while
> the simpler single char wildcard "_" isn't optimized to be faster.
> [https://github.com/apache/hive/blob/master/ql/src/java/org/apache/hadoop/hive/ql/exec/vector/expressions/AbstractFilterStringColLikeStringScalar.java]
> Has Begin, End, Middle and Chained checkers for "%", but no option to handle
> "_" in the chained mode.
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