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https://issues.apache.org/jira/browse/SOLR-3875?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13462210#comment-13462210
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Hoss Man commented on SOLR-3875:
--------------------------------
Committed revision 1389636. -4x
> 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
> Reporter: Toke Eskildsen
> Assignee: Hoss Man
> Priority: Critical
> Fix For: 4.0, 4.1, 5.0
>
> Attachments: SOLR-3875.patch
>
>
> 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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