SELECT 
  product_id, 
  feature_id, 
  variant_id 
FROM 
  cscart_product_features_values 
WHERE 
  product_id IN (
    431698, 431699, 431700, 431701, 431702, 
    431703, 431704, 431705, 431706, 431707, 
    431708, 431709, 431710, 431711, 431712, 
    431713, 431714, 431715, 431716, 431717, 
    431718, 431719, 431720, 431721, 431722, 
    431723, 431724, 431725, 431726, 431727, 
    431728, 431729, 431730, 431731, 431732, 
    431733
  ) 
  AND feature_id IN (626, 860) 
  AND lang_code = 'en'

Query time 0.00305

JSON explain

{
  "query_block": {
    "select_id": 1,
    "cost_info": {
      "query_cost": "29.99"
    },
    "table": {
      "table_name": "cscart_product_features_values",
      "access_type": "range",
      "possible_keys": [
        "PRIMARY",
        "fl",
        "lang_code",
        "product_id",
        "fpl",
        "idx_product_feature_variant_id"
      ],
      "key": "lang_code",
      "used_key_parts": [
        "lang_code",
        "feature_id",
        "product_id"
      ],
      "key_length": "12",
      "rows_examined_per_scan": 72,
      "rows_produced_per_join": 72,
      "filtered": "100.00",
      "using_index": true,
      "cost_info": {
        "read_cost": "15.59",
        "eval_cost": "14.40",
        "prefix_cost": "29.99",
        "data_read_per_join": "55K"
      },
      "used_columns": [
        "feature_id",
        "product_id",
        "variant_id",
        "lang_code"
      ],
      "attached_condition": "((`webmarco`.`cscart_product_features_values`.`product_id` in (431698,431699,431700,431701,431702,431703,431704,431705,431706,431707,431708,431709,431710,431711,431712,431713,431714,431715,431716,431717,431718,431719,431720,431721,431722,431723,431724,431725,431726,431727,431728,431729,431730,431731,431732,431733)) and (`webmarco`.`cscart_product_features_values`.`feature_id` in (626,860)) and (`webmarco`.`cscart_product_features_values`.`lang_code` = 'en'))"
    }
  }
}