SELECT 
  product_id, 
  feature_id, 
  variant_id 
FROM 
  cscart_product_features_values 
WHERE 
  product_id IN (
    7108, 7109, 7224, 7225, 7246, 7245, 7268, 
    7267, 7271, 7270, 6844, 6854, 3307, 
    6864, 6860, 6855, 3317, 3313, 3862, 
    3315
  ) 
  AND feature_id IN (
    628, 595, 641, 637, 636, 627, 623, 622, 
    626, 553, 625, 624
  ) 
  AND lang_code = 'en'

Query time 0.00698

JSON explain

{
  "query_block": {
    "select_id": 1,
    "cost_info": {
      "query_cost": "54.33"
    },
    "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": 240,
      "rows_produced_per_join": 240,
      "filtered": "100.00",
      "using_index": true,
      "cost_info": {
        "read_cost": "30.33",
        "eval_cost": "24.00",
        "prefix_cost": "54.33",
        "data_read_per_join": "185K"
      },
      "used_columns": [
        "feature_id",
        "product_id",
        "variant_id",
        "lang_code"
      ],
      "attached_condition": "((`gaseus`.`cscart_product_features_values`.`product_id` in (7108,7109,7224,7225,7246,7245,7268,7267,7271,7270,6844,6854,3307,6864,6860,6855,3317,3313,3862,3315)) and (`gaseus`.`cscart_product_features_values`.`feature_id` in (628,595,641,637,636,627,623,622,626,553,625,624)) and (`gaseus`.`cscart_product_features_values`.`lang_code` = 'en'))"
    }
  }
}