SELECT 
  cscart_products.*, 
  cscart_products.ebay_status, 
  cscart_products.ebay_template_id 
FROM 
  cscart_products 
WHERE 
  cscart_products.product_id IN (
    20829, 20830, 20831, 20832, 20833, 20834, 
    20835, 20836, 20837, 20838, 20839, 
    20840, 20841, 20842, 20843, 20844
  )

Query time 0.00035

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 (20829,20830,20831,20832,20833,20834,20835,20836,20837,20838,20839,20840,20841,20842,20843,20844)"
    }
  }
}