请问BM25相关度算法在es6.4上面是默认的吗？

{"settings":{"index":{

    "similarity": {

        "my_custom_similarity": {

            "discount_overlaps": "false",

            "b": "0.75",

            "type": "BM25",

            "k1": "1.2"

        }

    }

}}}





{

    "field_name":{

        "type":"text",

        "similarity":"my_custom_similarity"

    }

}