SELECT 
  cscart_products.*, 
  cscart_products.ebay_status, 
  cscart_products.ebay_template_id 
FROM 
  cscart_products 
WHERE 
  cscart_products.product_id IN (
    21983, 21984, 21985, 21986, 21987, 21988, 
    21989, 21990, 21991, 21992, 21993, 
    21994, 21995, 21996, 21997, 21998
  )

Query time 0.00037

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 (21983,21984,21985,21986,21987,21988,21989,21990,21991,21992,21993,21994,21995,21996,21997,21998)"
    }
  }
}