SELECT 
  cscart_products.* 
FROM 
  cscart_products 
WHERE 
  cscart_products.product_id IN (
    6508, 6502, 6504, 6507, 6505, 6506, 6501, 
    6503
  )

Query time 0.00027

JSON explain

{
  "query_block": {
    "select_id": 1,
    "table": {
      "table_name": "cscart_products",
      "access_type": "range",
      "possible_keys": ["PRIMARY"],
      "key": "PRIMARY",
      "key_length": "3",
      "used_key_parts": ["product_id"],
      "rows": 8,
      "filtered": 100,
      "index_condition": "cscart_products.product_id in (6508,6502,6504,6507,6505,6506,6501,6503)"
    }
  }
}