lucene2.4源码学习9 搜索 norm

 public float score() {
    int f = freqs[pointer];
    float raw =                                   // compute tf(f)*weight
      f < SCORE_CACHE_SIZE                        // check cache
      ? scoreCache[f]                             // cache hit
      : getSimilarity().tf(f)*weightValue;        // cache miss

    return raw * Similarity.decodeNorm(norms[doc]); // normalize for field
  }

计算得分的时候要用到norm。这个norm是怎么来的呢

 public Scorer scorer(IndexReader reader) throws IOException {
      TermDocs termDocs = reader.termDocs(term);

      if (termDocs == null)
        return null;

      return new TermScorer(this, termDocs, similarity,
                            reader.norms(term.field()));
    }

看到score是从reader中来的。


norm是在SegmentReader的openNorms设置的。

 private void openNorms(Directory cfsDir, int readBufferSize) throws IOException {
    long nextNormSeek = SegmentMerger.NORMS_HEADER.length; //skip header (header unused for now)
    int maxDoc = maxDoc();
    for (int i = 0; i < fieldInfos.size(); i++) {
      FieldInfo fi = fieldInfos.fieldInfo(i);
      if (norms.containsKey(fi.name)) {
        // in case this SegmentReader is being re-opened, we might be able to
        // reuse some norm instances and skip loading them here
        continue;
      }
      if (fi.isIndexed && !fi.omitNorms) {
        Directory d = directory();
        String fileName = si.getNormFileName(fi.number);
        if (!si.hasSeparateNorms(fi.number)) {
          d = cfsDir;
        }
        
        // singleNormFile means multiple norms share this file
        boolean singleNormFile = fileName.endsWith("." + IndexFileNames.NORMS_EXTENSION);
        IndexInput normInput = null;
        long normSeek;

        if (singleNormFile) {
          normSeek = nextNormSeek;
          if (singleNormStream==null) {
            singleNormStream = d.openInput(fileName, readBufferSize);
          }
          // All norms in the .nrm file can share a single IndexInput since
          // they are only used in a synchronized context.
          // If this were to change in the future, a clone could be done here.
          normInput = singleNormStream;
        } else {
          normSeek = 0;
          normInput = d.openInput(fileName);
        }

        norms.put(fi.name, new Norm(normInput, singleNormFile, fi.number, normSeek));
        nextNormSeek += maxDoc; // increment also if some norms are separate
      }
    }
  }