SELECT 
  cscart_products.*, 
  cscart_products.ebay_status, 
  cscart_products.ebay_template_id 
FROM 
  cscart_products 
WHERE 
  cscart_products.product_id IN (
    21053, 21054, 21055, 21056, 21057, 21058, 
    21059, 21060, 21061, 21062, 21063, 
    21064, 21065, 21066, 21067, 21068
  )

Query time 0.00043

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 (21053,21054,21055,21056,21057,21058,21059,21060,21061,21062,21063,21064,21065,21066,21067,21068)"
    }
  }
}