[GitHub] [solr] dsmiley commented on pull request #151: SOLR-15437: ReRanking/LTR does not work in combination with custom sort and SolrCloud

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dsmiley commented on pull request #151:
URL: https://github.com/apache/solr/pull/151#issuecomment-1055672942


   I ran into this problem today -- I'm glad others are working on it.  Unless I've misattributed this issue, I think this problem is not related to a "custom sort" -- one only needs to have a re-ranking boost function that could reduce the score from what it was.  QueryComponent.mergeIds doesn't know how to deal with scores that don't descend when you're sorting by score (as is the default).
   
   The solution above is one approach and I think it's basically fine.  It assumes that `rr.rows` docs across all shards are more relevant than all docs that follow, which I don't think is necessarily true, although it usually is when your data is balanced across the shards, as is typical.  Another solution is to have the ReRankQuery machinery apply a constant factor to the score of all docs that follow `rr.rows`, so that the scores continue to descend.  The factor could be computed based on how close the scores were between these documents on the fence prior to reranking, and then it could apply it proportionally to whatever the final score is of the last re-ranked document.


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