Score values different than Lucene ones

[Christian_Salvanesch (Christian Salvaneschi)]

Hi,

we are migrating from Lucene to ElasticSearch. We use "query_string" in order to execute the same (almost) queries we did previously on Lucene.
Queries works good, but the _score provided is pretty different than the Lucene one. It is not only the value itself but the sorting order results different.

Is the scoring on Elastic expected to be the same as Lucene? It seems so by reading documentation. Is there some special configuration to achieve this?

I tried changing "score_mode" and "boost_mode" in the "function_score" part but without luck.

Here a query example:

{
  "from": 0,
  "query": {
    "function_score": {
      "score_mode": "sum",
      "boost_mode": "sum",
      "functions": [
        {
          "field_value_factor": {
            "field": "Boost"
          }
        }
      ],
      "query": {
        "query_string": {
          "query": "... my query in Lucene query syntax..."
        }
      }
    }
  },
  "size": 10,
  "sort": [
    {
      "_score": {
        "order": "desc"
      }
    }
  ]
}