SELECT 
  product_id, 
  feature_id, 
  variant_id 
FROM 
  cscart_product_features_values 
WHERE 
  product_id IN (
    19102, 55711, 55712, 55713, 55714, 55715, 
    55716, 55717, 55718, 55719, 55720, 
    55721, 55722, 55723, 55724, 55725, 
    55726, 55727, 55728, 55729, 55730, 
    55731, 55732, 55733, 55734, 55735, 
    55736, 55737, 55738, 55739, 55740, 
    55741, 55742, 55743, 55744, 55745, 
    55746, 55747, 55748, 55749, 55750, 
    55751, 55752, 55753, 55754, 55755, 
    55756, 55757, 55758, 55759, 55760, 
    55761, 55762, 55763, 55764, 55765, 
    55766, 55767, 55768, 55769
  ) 
  AND feature_id IN (345, 1393) 
  AND lang_code = 'en'

Query time 0.00361

JSON explain

{
  "query_block": {
    "select_id": 1,
    "cost_info": {
      "query_cost": "6.62"
    },
    "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": "PRIMARY",
      "used_key_parts": [
        "feature_id",
        "product_id",
        "variant_id",
        "lang_code"
      ],
      "key_length": "15",
      "rows_examined_per_scan": 13,
      "rows_produced_per_join": 13,
      "filtered": "100.00",
      "using_index_for_skip_scan": true,
      "cost_info": {
        "read_cost": "5.32",
        "eval_cost": "1.30",
        "prefix_cost": "6.62",
        "data_read_per_join": "10K"
      },
      "used_columns": [
        "feature_id",
        "product_id",
        "variant_id",
        "lang_code"
      ],
      "attached_condition": "((`cscartdb`.`cscart_product_features_values`.`product_id` in (19102,55711,55712,55713,55714,55715,55716,55717,55718,55719,55720,55721,55722,55723,55724,55725,55726,55727,55728,55729,55730,55731,55732,55733,55734,55735,55736,55737,55738,55739,55740,55741,55742,55743,55744,55745,55746,55747,55748,55749,55750,55751,55752,55753,55754,55755,55756,55757,55758,55759,55760,55761,55762,55763,55764,55765,55766,55767,55768,55769)) and (`cscartdb`.`cscart_product_features_values`.`feature_id` in (345,1393)) and (`cscartdb`.`cscart_product_features_values`.`lang_code` = 'en'))"
    }
  }
}