SELECT 
  product_id, 
  feature_id, 
  variant_id 
FROM 
  cscart_product_features_values 
WHERE 
  product_id IN (
    431615, 431616, 431617, 431618, 431619, 
    431620, 431621, 431622, 431623, 431624, 
    431625, 431626, 431627, 431628, 431629, 
    431630, 431631, 431632, 431633, 431634, 
    431635, 431636, 431637, 431638, 431639, 
    431640, 431641, 431642, 431643, 431644, 
    431645, 431646, 431647, 431648, 431649, 
    431650, 431651, 431652, 431653, 431654, 
    431655, 431656, 431657, 431658
  ) 
  AND feature_id IN (626, 860) 
  AND lang_code = 'en'

Query time 0.00646

JSON explain

{
  "query_block": {
    "select_id": 1,
    "cost_info": {
      "query_cost": "36.43"
    },
    "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": 88,
      "rows_produced_per_join": 88,
      "filtered": "100.00",
      "using_index": true,
      "cost_info": {
        "read_cost": "18.83",
        "eval_cost": "17.60",
        "prefix_cost": "36.43",
        "data_read_per_join": "68K"
      },
      "used_columns": [
        "feature_id",
        "product_id",
        "variant_id",
        "lang_code"
      ],
      "attached_condition": "((`webmarco`.`cscart_product_features_values`.`product_id` in (431615,431616,431617,431618,431619,431620,431621,431622,431623,431624,431625,431626,431627,431628,431629,431630,431631,431632,431633,431634,431635,431636,431637,431638,431639,431640,431641,431642,431643,431644,431645,431646,431647,431648,431649,431650,431651,431652,431653,431654,431655,431656,431657,431658)) and (`webmarco`.`cscart_product_features_values`.`feature_id` in (626,860)) and (`webmarco`.`cscart_product_features_values`.`lang_code` = 'en'))"
    }
  }
}