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From "Toke Eskildsen (JIRA)" <j...@apache.org>
Subject [jira] [Created] (SOLR-3875) Document boost does not work correctly when using multi-valued fields
Date Mon, 24 Sep 2012 13:41:07 GMT
Toke Eskildsen created SOLR-3875:
------------------------------------

             Summary: Document boost does not work correctly when using multi-valued fields
                 Key: SOLR-3875
                 URL: https://issues.apache.org/jira/browse/SOLR-3875
             Project: Solr
          Issue Type: Bug
          Components: Schema and Analysis, update
    Affects Versions: 4.0-BETA, 4.0, 4.1, 5.0
            Reporter: Toke Eskildsen
             Fix For: 4.0, 4.1, 5.0, 4.0-BETA


In Solr 4 BETA & trunk, document boosts skews the ranking for documents with multi value
fields tremendously. A document boost of 5 combined with 15 values in a multi value field
results in scores above 1,000,000,000, while a boost of 0,5 results in scores below 0,001.
The error is not present in Solr 3.6.

Thomas Egense and I have tracked it down to a change in Solr DocumentBuilder committed 20110827
(@1162347) by Mike McCandless, as part of work done on LUCENE-2308. The problem is that Lucene
multiplies the boosts of multiple instances of the same field when updating the index.

The old DocumentBuilder, used in Lucene 3.6, handled this by calculating the score for the
field (docBoost*fieldBoost) and assigning it to the first instance of the field, then setting
the boost to 1.0f and assigning that to subsequent instances of the field. This effectively
assigned docBoost*fieldBoost to the field, regardless of the number of instances.

The updated DocumentBuilder (see https://svn.apache.org/viewvc/lucene/dev/branches/lucene_solr_4_0/solr/core/src/java/org/apache/solr/update/DocumentBuilder.java?revision=1388778&view=markup),
used in Lucene 4 BETA & trunk, also assigns docBoost*fieldBoost to the first instance
of the field. Then it sets fieldBoost = docBoost and continues to assign docBoost*fieldBoost
to subsequent instances. Using the example mentioned above, the generated IndexableFields
will get assigned boosts of 5, 5*5, 5*5... 5*5. As Lucene multiplies all the values, 15 instances
of the same field will have a collective boost of 5*25^14.

This can be demonstrated with the Solr tutorial example by indexing the sample documents and
adding the document 
{code:xml}
<add>
<doc boost="5">
  <field name="id">Insane score Example. Score = 10E9 </field>
  <field name="name">Document boost broken for multivalued fields</field>
  <field name="manu">Thomas Egense and Toke Eskildsen</field>
  <field name="manu_id_s">Test</field>
  <field name="cat">bug</field>
  <field name="features">insane_boost</field>
  <field name="features">something else</field>
  <field name="features">something else</field>
  <field name="features">something else</field>
  <field name="features">something else</field>
  <field name="features">something else</field>
  <field name="features">something else</field>
  <field name="features">something else</field>
  <field name="features">something else</field>
  <field name="features">something else</field>
  <field name="features">something else</field>
  <field name="features">something else</field>
  <field name="features">something else</field>
  <field name="features">something else</field>  
</doc>
</add>
{code}

The _manu_ & _features_-fields gets copied to _text_ and a search for _thomas_ matches
the _text_-field with query explanation
{code:xml}
<str name="Insane score Example. Score = 10E10 ">
2.44373361E10 = (MATCH) weight(text:thomas in 0) [DefaultSimilarity], result of:
  2.44373361E10 = fieldWeight in 0, product of:
    1.0 = tf(freq=1.0), with freq of:
      1.0 = termFreq=1.0
    3.2512918 = idf(docFreq=3, maxDocs=38)
    7.5161928E9 = fieldNorm(doc=0)
</str>
{code}

Thomas and I are too pressed for time to attempt a proper patch at the moment, but we guess
that a reversion to the old algorithm of assigning the combined boost to the first instance
and 1.0f to all subsequent instances would work?

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