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  1. Lucene - Core
  2. LUCENE-7337

MultiTermQuery are sometimes rewritten into an empty boolean query


    • Bug
    • Status: Closed
    • Minor
    • Resolution: Fixed
    • None
    • 6.2, 7.0
    • core/search
    • None
    • New


      MultiTermQuery are sometimes rewritten to an empty boolean query (depending on the rewrite method), it can happen when no expansions are found on a fuzzy query for instance.
      It can be problematic when the multi term query is boosted.
      For instance consider the following query:

      `((title:bar~1)^100 text:bar)`

      This is a boolean query with two optional clauses. The first one is a fuzzy query on the field title with a boost of 100.
      If there is no expansion for "title:bar~1" the query is rewritten into:

      `(()^100 text:bar)`

      ... and when expansions are found:

      `((title:bars | title:bar)^100 text:bar)`

      The scoring of those two queries will differ because the normalization factor and the norm for the first query will be equal to 1 (the boost is ignored because the empty boolean query is not taken into account for the computation of the normalization factor) whereas the second query will have a normalization factor of 10,000 (100*100) and a norm equal to 0.01.

      This kind of discrepancy can happen in a single index because the expansions for the fuzzy query are done at the segment level. It can also happen when multiple indices are requested (Solr/ElasticSearch case).

      A simple fix would be to replace the empty boolean query produced by the multi term query with a MatchNoDocsQuery but I am not sure that it's the best way to fix. WDYT ?


        1. LUCENE-7337.patch
          9 kB
          Michael McCandless



            Unassigned Unassigned
            jim.ferenczi Jim Ferenczi
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