[jira] [Resolved] (HBASE-28905) Skip excessive evaluations of LINK_NAME_PATTERN and REF_NAME_PATTERN regular expressions

["Wellington Chevreuil (Jira)" <ji...@apache.org>]

     [ https://issues.apache.org/jira/browse/HBASE-28905?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel ]

Wellington Chevreuil resolved HBASE-28905.
------------------------------------------
    Resolution: Fixed

Merged into master, branch-3, branch-2 and branch-2.6. Thanks for the contribution, [~charlesconnell] !

> Skip excessive evaluations of LINK_NAME_PATTERN and REF_NAME_PATTERN regular expressions
> ----------------------------------------------------------------------------------------
>
>                 Key: HBASE-28905
>                 URL: https://issues.apache.org/jira/browse/HBASE-28905
>             Project: HBase
>          Issue Type: Improvement
>    Affects Versions: 2.6.0, 3.0.0-beta-1, 2.7.0
>            Reporter: Charles Connell
>            Assignee: Charles Connell
>            Priority: Minor
>              Labels: pull-request-available
>             Fix For: 3.0.0, 2.7.0, 2.6.1
>
>         Attachments: cpu_time_flamegraph_2.6.0.html, cpu_time_flamegraph_with_optimization.html, performance_test_query_latency_2.6.0.png, performance_test_query_latency_with_optimization.png
>
>
> To test if a file is a link file, HBase checks if its file name matches the regex
> {code:java}
> ^(?:((?:[_\p{Digit}\p{IsAlphabetic}]+))(?:\=))?((?:[_\p{Digit}\p{IsAlphabetic}][-_.\p{Digit}\p{IsAlphabetic}]*))=((?:[a-f0-9]+))-([0-9a-f]+(?:(?:_SeqId_[0-9]+_)|(?:_del))?)$
> {code}
> To test if an HFile has a "reference name," HBase checks if its file name matches the regex
> {code:java}
> ^([0-9a-f]+(?:(?:_SeqId_[0-9]+_)|(?:_del))?|^(?:((?:[_\p{Digit}\p{IsAlphabetic}]+))(?:\=))?((?:[_\p{Digit}\p{IsAlphabetic}][-_.\p{Digit}\p{IsAlphabetic}]*))=((?:[a-f0-9]+))-([0-9a-f]+(?:(?:_SeqId_[0-9]+_)|(?:_del))?)$)\.(.+)$
> {code}
> Matching against these big regexes is computationally expensive. HBASE-27474 introduced (in 2.6.0) [code in a hot path|https://github.com/apache/hbase/blob/1602c531b245b4d455b48161757cde2ec3d1930b/hbase-server/src/main/java/org/apache/hadoop/hbase/io/hfile/HFileReaderImpl.java#L1716] in {{HFileReaderImpl}} that checks whether an HFile is a link or reference file while deciding whether to cache blocks from that file. In flamegraphs taken at my company during performance tests, this meant that these regex evaulations take 2-3% of the CPU time on a busy RegionServer.
> Later, the hot-path invocation of the regexes was removed in HBASE-28596 in branch-2 and later, but not branch-2.6, so only the 2.6.x series suffers the performance regression. Nonetheless, all invocations of these regexes are still unnecessarily expensive and can be fast-failed easily.
> The link name pattern contains a literal "=", so any string that does not contain a "=" can be assumed to not match the regex. The reference name pattern contains a literal ".", so any string that does not contain a "." can be assumed to not match the regex. This optimization is mostly helpful in 2.6.x, but is valid in all branches.
> Running performance tests of this optimization removed the regex evaluations from my flamegraphs entirely, and reduced query latency by 15%. Some charts are attached.



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