Question

I am trying to boost particular documents based on a field value. It is generally working ok but some documents return a higher score even though they have a smaller boost value.

After debugging the query with the debugQuery=on request parameter I have noticed that the idf function is returning a higher score for a particular document, which is affecting the overall score.

Is there a way to ignore tf/idf scoring at query time?

Answer 1

You’ll want to create a custom Similarity which overrides the tf and idf methods, and use it in place of the DefaultSimilarity.

Something like:

class CustomSimilarity extends DefaultSimilarity {

    @Override
    public float tf(float freq) {
        return 1.0;
    }

    @Override
    public float tf(int freq) {
        return 1.0;
    }

    @Override
    // Note the signature of this method may now take longs:
    //   public float idf(long docFreq, long numDocs)
    public float idf(int docFreq, int numDocs) {
        return 1.0;
    }
}

The set it to use that similarity in your schema.xml:

<similarity class="myorg.mypackage.CustomSimilarity"/>