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From "Jordi Salvat i Alabart (Created) (JIRA)" <>
Subject [jira] [Created] (LUCENE-3957) Document precision requirements of setBoost calls
Date Thu, 05 Apr 2012 10:05:25 GMT
Document precision requirements of setBoost calls

                 Key: LUCENE-3957
             Project: Lucene - Java
          Issue Type: Improvement
          Components: general/javadocs
    Affects Versions: 3.5
            Reporter: Jordi Salvat i Alabart

The behaviour of index-time boosts seems pretty erratic (e.g. a boost of 8.0 produces the
exact same score as a boost of 9.0) until you become aware that these factors end up encoded
in a single byte, with a three-bit mantissa. This consumed a whole day of research for us,
and I still believe we were lucky to spot it, given how deeply dug into the code & documentation
this information is.

I suggest adding a small note to the JavaDoc of setBoost methods in Document, Fieldable, FieldInvertState,
and possibly AbstractField, Field, and NumericField.

Suggested text:
"Note that all index-time boost values end up encoded using Similarity.encodeNormValue, with
a 3-bit mantissa -- so differences in the boost value of less than 25% may easily be rounded

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