SELECT 
  cscart_products.*, 
  cscart_products.ebay_status, 
  cscart_products.ebay_template_id 
FROM 
  cscart_products 
WHERE 
  cscart_products.product_id IN (
    21181, 21182, 21183, 21184, 21185, 21186, 
    21187, 21188, 21189, 21190, 21191, 
    21192, 21193, 21194, 21195, 21196
  )

Query time 0.00031

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 (21181,21182,21183,21184,21185,21186,21187,21188,21189,21190,21191,21192,21193,21194,21195,21196)"
    }
  }
}