[jira] [Created] (SPARK-59389) Avoid per-character UTF8String allocation in trimLeft/trimRight with a trim set

["David Mollitor (Jira)" <ji...@apache.org>]

David Mollitor created SPARK-59389:
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             Summary: Avoid per-character UTF8String allocation in trimLeft/trimRight with a trim set
                 Key: SPARK-59389
                 URL: https://issues.apache.org/jira/browse/SPARK-59389
             Project: Spark
          Issue Type: Improvement
          Components: Spark Core
    Affects Versions: 4.1.0
            Reporter: David Mollitor


h2. Summary

The trim overloads that take a set of trim characters -- {{trimLeft(UTF8String)}} and
{{trimRight(UTF8String)}}, with {{trim(UTF8String)}} delegating to both -- allocate a throwaway {{UTF8String}} for every source character they examine. Each iteration calls {{copyUTF8String(...)}} (a {{new byte[]}} + {{copyMemory}} + {{fromBytes}}) only to pass that one character to {{trimString.find(searchChar, 0)}}. Trimming k leading/trailing characters does O(k) heap allocations.

The character under test is already a byte range in this string's backing memory, so the
membership check can read it directly. This factors {{find}} to accept a raw
{{(base, offset, numBytes)}} needle and calls it on the source character's bytes in place, so the O(k) allocations become O(1). Performance-only; behavior is identical.



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