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From "Yonik Seeley (JIRA)" <>
Subject [jira] Created: (LUCENE-448) optional norms
Date Sat, 08 Oct 2005 15:58:47 GMT
optional norms

         Key: LUCENE-448
     Project: Lucene - Java
        Type: New Feature
  Components: Index  
    Versions: CVS Nightly - Specify date in submission    
    Reporter: Yonik Seeley
 Attachments: omitNorms.txt

For applications with many indexed fields, the norms cause memory problems both during indexing
and querying.
This patch makes norms optional on a per-field basis, in the same way that term vectors are
optional per-field.

Overview of changes:
 - Field.omitNorms that defaults to false
 - backward compatible lucene file format change: FieldInfos.FieldBits has a bit for omitNorms
 - IndexReader.hasNorms() method
 - During merging, if any segment includes norms, then norms are included.
 - methods to get norms return the equivalent 1.0f array for backward compatibility

The patch was designed for backward compatibility:
 - all current unit tests pass w/o any modifications required
 - compatible with old indexes since the default is omitNorms=false
 - compatible with older/custom subclasses of IndexReader since a default hasNorms() is provided
 - compatible with older/custom users of IndexReader such as Weight/Scorer/explain since a
norm array is produced on demand, even if norms were not stored

If this patch is accepted (or if the direction is acceptable), performance for scoring  could
be improved by assuming 1.0f when hasNorms(field)==false.

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