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https://issues.apache.org/jira/browse/LUCENE-3957?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13256736#comment-13256736
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Jordi Salvat i Alabart commented on LUCENE-3957:
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Wherever, but please increase exposure of this detail, for the sake of those
who're coming in later.
It's a VERY long and winded way between setting a $docBoost in a SolR
dataSource transformer script and the current location of this information.
Would be kind of acceptable if the value was held with a couple of decimal
digits of precision, but the default (3-bit) implementation doesn't hold even
ONE digit, making the behaviour really shocking -- specially since the boost
value is not directly visible, but only through its impact on search scores.
> Document precision requirements of setBoost calls
> -------------------------------------------------
>
> Key: LUCENE-3957
> URL: https://issues.apache.org/jira/browse/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 away."
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