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https://issues.apache.org/jira/browse/IMPALA-12374?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
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Balazs Hevele reassigned IMPALA-12374:
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Assignee: Balazs Hevele
> Explore optimizing re2 usage for leading / trailing ".*" when generating LIKE
> regex
> -----------------------------------------------------------------------------------
>
> Key: IMPALA-12374
> URL: https://issues.apache.org/jira/browse/IMPALA-12374
> Project: IMPALA
> Issue Type: Improvement
> Components: Backend
> Affects Versions: Impala 4.3.0
> Reporter: Joe McDonnell
> Assignee: Balazs Hevele
> Priority: Major
> Labels: ramp-up
>
> Abseil has some recommendations about efficiently using re2 here:
> [https://abseil.io/fast/21]
> One recommendation it has is to avoid leading / trailing .* for FullMatch():
> {noformat}
> Using RE2::FullMatch() with leading or trailing .* is an antipattern.
> Instead, change it to RE2::PartialMatch() and remove the .*.
> RE2::PartialMatch() performs an unanchored search, so it is also necessary to
> anchor the regular expression (i.e. with ^ or $) to indicate that it must
> match at the start or end of the string.{noformat}
> For our slow path LIKE evaluation, we convert the LIKE to a regular
> expression and use FullMatch(). Our code to generate the regular expression
> will use leading/trailing .* and FullMatch for patterns like '%a%b%'. We
> could try detecting these cases and switching to PartialMatch with anchors.
> See the link for more details about how this works.
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