[jira] [Created] (IMPALA-12374) Explore optimizing re2 usage for leading / trailing ".*"

["Joe McDonnell (Jira)" <ji...@apache.org>]

Joe McDonnell created IMPALA-12374:
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             Summary: Explore optimizing re2 usage for leading / trailing ".*"
                 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


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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