[SOLR-13838] igain query parser generating invalid output

• Type: Bug
• Status: Open
• Priority: Major
• Resolution: Unresolved
• Affects Version/s: 8.2
• Component/s: query parsers

Environment

The issue is a generic Java defect and therefore will be independent of the operating system or software platform.

• Assignee: Unassigned
• Reporter: Peter Davie
• Created: 12/Oct/19 04:38
• Updated: 21/Jan/20 16:57

Description

Investigating the output from the "features()" stream source, terms are being returned with NaN for the score_f field:

{{    "docs": [}}
{{      {}}
{{        "featureSet_s": "business",}}
{{        "score_f": "NaN",}}
{{        "term_s": "1,011.15",}}
{{        "idf_d": "-Infinity",}}
{{        "index_i": 1,}}
{{        "id": "business_1"}}
{{      },}}
{{      {}}
{{        "featureSet_s": "business",}}
{{        "score_f": "NaN",}}
{{        "term_s": "10.3m",}}
{{        "idf_d": "-Infinity",}}
{{        "index_i": 2,}}
{{        "id": "business_2"}}
{{      },}}
{{      {}}
{{        "featureSet_s": "business",}}
{{        "score_f": "NaN",}}
{{        "term_s": "01",}}
{{        "idf_d": "-Infinity",}}
{{        "index_i": 3,}}
{{        "id": "business_3"}}
{{      },...}}

Looking into{{ org/apache/solr/search/IGainTermsQParserPlugin.java}}, it seems that when a term is not included in the positive or negative documents, the docFreq calculation (docFreq = xc + nc) is 0, which means that subsequent calculations result in NaN (division by 0).

Attached is a patch which skips terms for which docFreq
is 0 in the finish() method of IGainTermsQParserPlugin and this resolves the issues with NaN scores in the features() output.