Impossible to use custom norm encoding/decoding
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Key: LUCENE-1261
URL: https://issues.apache.org/jira/browse/LUCENE-1261
Project: Lucene - Java
Issue Type: Bug
Components: Query/Scoring
Affects Versions: 2.3.1
Environment: All
Reporter: John Adams
Although it is possible to override methods encodeNorm and decodeNorm in a
custom Similarity class, these methods are not actually used by the query
processing and scoring functions, not by the indexing functions. The relevant
Lucene classes all call "Similarity.decodeNorm" rather than
"similarity.decodeNorm", i.e. the norm encoding/decoding is fixed to use that
of the base Similarity class. Also index writing classes such as DocumentWriter
use "Similarity.decodeNorm" rather than "similarity.decodeNorm", so we are
stuck with the 3 bit mantissa encoding implemented by SmallFloat.floatToByte315
and SmallFloat.byte315ToFloat.
This is very restrictive and annoying, since in practice many users would
prefer an encoding that allows finer distinctions for boost and normalisation
factors close to 1.0. For example. SmallFloat.floatToByte52 uses 5 bits of
mantissa, and this would be of great help in distinguishing much better between
subtly different lengthNorms and FieldBoost/DocumentBoost values.
It hsould be easy to fix this by changing all instances of
"Similarity.decodeNorm" and "Similarity.encodeNorm" to "similarity.decodeNorm"
and "similarity.encodeNorm" in the Lucene code (there are only a few of each).
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