What is disadvantages of query database smart service

I will not say those are disadvantages as others have mentioned earlier. Each serve its purpose.

The main difference would be that when querying from records, you are trying to get the data from the memory i.e., cache which gives you a quicker response. Also you would not perform a direct query on the database.

Heres something from the documentation which will make it clear

"Data sync caches your source data in Appian.

Think of it like a cache on your web browser: when you cache web content locally on your browser, your site content loads faster and improves the speed of your browsing. The same applies when you sync your source data—Appian only has to execute queries against your synced data instead of the external source, so your record data will load faster. In addition to faster queries"

https://docs.appian.com/suite/help/22.2/records-data-sync.html#how-does-data-sync-work

I will not say those are disadvantages as others have mentioned earlier. Each serve its purpose.

The main difference would be that when querying from records, you are trying to get the data from the memory i.e., cache which gives you a quicker response. Also you would not perform a direct query on the database.

Heres something from the documentation which will make it clear

"Data sync caches your source data in Appian.

Think of it like a cache on your web browser: when you cache web content locally on your browser, your site content loads faster and improves the speed of your browsing. The same applies when you sync your source data—Appian only has to execute queries against your synced data instead of the external source, so your record data will load faster. In addition to faster queries"

https://docs.appian.com/suite/help/22.2/records-data-sync.html#how-does-data-sync-work