[GitHub] [arrow-datafusion] yjshen commented on issue #2557: [Question] why need this sort in Sort.rs

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yjshen commented on issue #2557:
URL: https://github.com/apache/arrow-datafusion/issues/2557#issuecomment-1131011698

   `group_indices` takes adjacent records in the same batch as input, and does best-effort grouping to make slices instead of individual positions for better `extend` performance (extend a range of records rather than individual record at a time).
   
    `sort_unstable` is useful since the positions are generated from `lexsort` which is unstable itself. there would be a possibility that records with the same sort key appear randomly after `lexsort`.  but `extend` takes start pos and length as input, so a sort to make records with the same sort key appears sequentially is needed.


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