SELECT 
  cscart_products.*, 
  cscart_products.ebay_status, 
  cscart_products.ebay_template_id 
FROM 
  cscart_products 
WHERE 
  cscart_products.product_id IN (
    21229, 21230, 21231, 21232, 21233, 21234, 
    21235, 21236, 21237, 21238, 21239, 
    21240, 21241, 21242, 21243, 21244
  )

Query time 0.00031

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 (21229,21230,21231,21232,21233,21234,21235,21236,21237,21238,21239,21240,21241,21242,21243,21244)"
    }
  }
}