[jira] [Commented] (LUCENE-7337) MultiTermQuery are sometimes rewritten into an empty boolean query

["Michael McCandless (JIRA)" <ji...@apache.org>]

    [ https://issues.apache.org/jira/browse/LUCENE-7337?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15328362#comment-15328362 ] 

Michael McCandless commented on LUCENE-7337:
--------------------------------------------

bq. 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. 

+1

Or more generally can we have an empty-clause BQ rewrite to {{MatchNoDocsQuery}}?  I had folded this into my attempt to fix the world's-hardest-toString-issue (LUCENE-7276) but it was too many changes to try at once, so breaking it out here is great.

However, before we can do this, we need to fix {{MatchNoDocsQuery}} to not rewrite to an empty BQ else we get a never-terminating rewrite ;)

> MultiTermQuery are sometimes rewritten into an empty boolean query
> ------------------------------------------------------------------
>
>                 Key: LUCENE-7337
>                 URL: https://issues.apache.org/jira/browse/LUCENE-7337
>             Project: Lucene - Core
>          Issue Type: Bug
>          Components: core/search
>            Reporter: Ferenczi Jim
>            Priority: Minor
>
> 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 ?
>  



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