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https://issues.apache.org/jira/browse/LUCENE-3957?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13248215#comment-13248215
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Simon Willnauer commented on LUCENE-3957:
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bq. I don't think we should put docs there in those classes:
+1 thats a very long standing impl detail. If it is not on the wiki in the FAQ
we should add it or maybe add a pitfalls section to the wiki.
> 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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