Hello,
 
It basis on the configuration which you choose while setting up a platform server. 

•  https://success.outsystems.com/documentation/11/setup_and_maintain_your_outsystems_infrastructure/setting_up_outsystems/default_platform_server_and_database_configurations/

You can also refer to the Post here - 
https://www.outsystems.com/forums/discussion/46646/does-outsystem-has-its-internal-db-by-default-when-we-create-application-or-not/

Thanks
Tousif Khan

Hi Hora Susuki

I would suggest you to refer the following link below-

https://www.outsystems.com/forums/discussion/80308/what-database-does-outsystems-use-by-default/#:~:text=If%20you%20have%20a%20Google,infrastructure%20is%20provisioned%20for%20you

Hope this helps

Thanks