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  1. Apache Arrow
  2. ARROW-12725

[C++][Compute] GroupBy: improve performance by encoding keys in row format only when they are inserted into hash table

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Details

    • Improvement
    • Status: Resolved
    • Major
    • Resolution: Fixed
    • 4.0.0
    • 6.0.0
    • C++

    Description

      Previous implementation of hash group by converts input ExecBatches to row-oriented format,
      then hashes and compares rows as if they were a single column. 
      It is more efficient (especially for small number of key columns) to avoid relatively costly 
      encoding and instead compute hashes of individual columns in column-oriented format mixing them together, and similarly comparing column-oriented data to row-oriented data in the hash table without converting. 
      Encoding only happens for a subset of input rows that are inserted into the hash table - they introduce new groups. 
      Keys in hash table remain stored as row-oriented.

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            michalno Michal Nowakiewicz
            michalno Michal Nowakiewicz
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