SELECT 
  cscart_products.*, 
  cscart_products.ebay_status, 
  cscart_products.ebay_template_id 
FROM 
  cscart_products 
WHERE 
  cscart_products.product_id IN (
    20845, 20846, 20847, 20848, 20849, 20850, 
    20851, 20852, 20853, 20854, 20855, 
    20856, 20857, 20858, 20859, 20860
  )

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 (20845,20846,20847,20848,20849,20850,20851,20852,20853,20854,20855,20856,20857,20858,20859,20860)"
    }
  }
}