SELECT 
  cscart_products.*, 
  cscart_products.ebay_status, 
  cscart_products.ebay_template_id 
FROM 
  cscart_products 
WHERE 
  cscart_products.product_id IN (
    21293, 21294, 21295, 21296, 21297, 21298, 
    21299, 21300, 21301, 21302, 21303, 
    21304, 21305, 21306, 21307, 21308
  )

Query time 0.00048

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": 16,
      "filtered": 100,
      "index_condition": "cscart_products.product_id in (21293,21294,21295,21296,21297,21298,21299,21300,21301,21302,21303,21304,21305,21306,21307,21308)"
    }
  }
}