Function score and optional weight : avg score is wrong

[ghiron]

related to #7137 #6955

Score calculation is wrong when score mode is set to average :
Let's say we have :

• function A returns 25 and weight of 10
• function B returns 10 and weight of 5

returned value is (25 *10 +10 * 5 )/ 2 = 150
returned value should be (25 *10 +10 * 5 )/ (10 +5) = 20

I think problem is located in org.elasticsearch.common.lucene.search.function.FiltersFunctionScoreQuery:302

double totalFactor = 0.0f;
int count = 0;
for (int i = 0; i < filterFunctions.length; i++) {
   if (docSets[i].get(docId)) {
      totalFactor += filterFunctions[i].function.score(docId, subQueryScore);
      count++;
   }
}
if (count != 0) {
   factor = totalFactor;
   if (scoreMode == ScoreMode.Avg) {
      factor /= count;
   }
}

should be something like

double totalFactor = 0.0f;
float count = 0;
for (int i = 0; i < filterFunctions.length; i++) {
   if (docSets[i].get(docId)) {
      totalFactor += filterFunctions[i].function.score(docId, subQueryScore);
      if (filterFunctions[i].function instanceof WeightFactorFunction){
         count+= ((WeightFactorFunction)filterFunctions[i].function).getWeight();
      }else{
         count++;
      }
   }
}
if (count != 0) {
   factor = totalFactor;
   if (scoreMode == ScoreMode.Avg) {
      factor /= count;
   }
}

[rjernst]

Thanks @ghiron! Do you want to create a pull request with your change?

[ghiron]

I'm on it

[ghiron]

@rjernst : I'm updating tests and have negative weight in some tests. Does it really make sense to have negative weight ?

[rjernst]

@ghiron Which tests use negative weights?

[ghiron]

@rjernst in FunctionScoreTests createRandomWeights method returns negative value half of the time

An other comment about this test class : getRandomScoreMode method returns random score mode value but does not guarantee all values will be tested.
simpleWeightedFunctionsTestWithRandomWeightsAndRandomCombineMode test is the only place I found avg score mode test so basically avg computation is tested once over 5 execution