SELECT 
  product_id, 
  feature_id, 
  variant_id 
FROM 
  cscart_product_features_values 
WHERE 
  product_id IN (
    7494, 7495, 7498, 7499, 7504, 7505, 7526, 
    7527, 2219, 5227, 5226, 2217, 5225, 
    2218, 1525, 1524, 5817, 1523, 5818, 
    5819, 5238, 5240, 5237, 5239, 5241, 
    3732, 6449, 1543, 6448, 2864, 5242, 
    2863, 5243, 1517, 1520, 1518, 1519, 
    5224, 1541, 1537, 1540, 1544, 1545, 
    2735, 5244, 6322, 1521, 1522, 5223, 
    5220, 3729, 5221, 5222, 1538, 1539, 
    1542
  ) 
  AND feature_id IN (
    627, 623, 622, 626, 553, 625, 624, 628, 
    595
  ) 
  AND lang_code = 'en'

Query time 0.00703

JSON explain

{
  "query_block": {
    "select_id": 1,
    "cost_info": {
      "query_cost": "113.45"
    },
    "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": "idx_product_feature_variant_id",
      "used_key_parts": [
        "product_id",
        "feature_id",
        "lang_code"
      ],
      "key_length": "12",
      "rows_examined_per_scan": 504,
      "rows_produced_per_join": 504,
      "filtered": "100.00",
      "using_index": true,
      "cost_info": {
        "read_cost": "63.05",
        "eval_cost": "50.40",
        "prefix_cost": "113.45",
        "data_read_per_join": "389K"
      },
      "used_columns": [
        "feature_id",
        "product_id",
        "variant_id",
        "lang_code"
      ],
      "attached_condition": "((`gaseus`.`cscart_product_features_values`.`product_id` in (7494,7495,7498,7499,7504,7505,7526,7527,2219,5227,5226,2217,5225,2218,1525,1524,5817,1523,5818,5819,5238,5240,5237,5239,5241,3732,6449,1543,6448,2864,5242,2863,5243,1517,1520,1518,1519,5224,1541,1537,1540,1544,1545,2735,5244,6322,1521,1522,5223,5220,3729,5221,5222,1538,1539,1542)) and (`gaseus`.`cscart_product_features_values`.`feature_id` in (627,623,622,626,553,625,624,628,595)) and (`gaseus`.`cscart_product_features_values`.`lang_code` = 'en'))"
    }
  }
}