[GitHub] [lucene] dsmiley commented on pull request #426: Javadocs, Sorter impls:

[GitBox <gi...@apache.org>]

dsmiley commented on pull request #426:
URL: https://github.com/apache/lucene/pull/426#issuecomment-961979683


   > I think the quality of the in-place merge sort is to be stable, and more efficient (O(n.log(n)) on larger arrays than the binary sort or insertion sort (O(n2)).
   
   That's not useful advise to a user because we don't offer the latter two.  We offer MSBRadixSorter, IntroSorter, InPlaceMergeSorter and TimSorter.
   
   I'm approaching this from a user's perspective who doesn't work on sorting algorithms.  We have a number of options and they should have documentation that helps me/us decide which to used based on the situation.  The current docs and even with my minor changes are confusing.  Based on what I've found here so far, my thought-process is to choose a sorting algorithm based on this ranked list:
   1. Use MSBRadixSorter if I have strings (includes byte strings / arrays) and don't mind a non-stable sort.
   2. Use IntroSorter if I don't mind non-stable sort.  _(however I've seen a trick by Adrien in our code somewhere to work-around the lack of stability by adding a number to the sort criteria based on the original position.)_
   3. InPlaceMergeSorter if need a stable sort and the list to sort is typically small.  (this is my assessment; could be wrong).
   4. Use TimSorter otherwise
   
   If my characterization is sub-optimal, lets work out what advise to give in a similar fashion to the above and put this on Sorter's class javadocs so we have one place to point users.
   


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