SELECT 
  cscart_products.*, 
  cscart_products.ebay_status, 
  cscart_products.ebay_template_id 
FROM 
  cscart_products 
WHERE 
  cscart_products.product_id IN (
    21277, 21278, 21279, 21280, 21281, 21282, 
    21283, 21284, 21285, 21286, 21287, 
    21288, 21289, 21290, 21291, 21292
  )

Query time 0.00034

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 (21277,21278,21279,21280,21281,21282,21283,21284,21285,21286,21287,21288,21289,21290,21291,21292)"
    }
  }
}