SELECT 
  cscart_products.*, 
  cscart_products.ebay_status, 
  cscart_products.ebay_template_id 
FROM 
  cscart_products 
WHERE 
  cscart_products.product_id IN (
    21647, 21648, 21649, 21650, 21651, 21652, 
    21653, 21654, 21655, 21656, 21657, 
    21658, 21659, 21660, 21661, 21662
  )

Query time 0.00051

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 (21647,21648,21649,21650,21651,21652,21653,21654,21655,21656,21657,21658,21659,21660,21661,21662)"
    }
  }
}