Document precision requirements of setBoost calls
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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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