I’m a little bit lost from your question. There are more questions here and problematic combination with them.
Dynamic Configuration
Yes, you can use ets. Also you can use just GenServer and store it in memory. Some guy from the community create some hex package with nice GenServer logic of configuration, but I can not find it now. But it will work only with your applications, or you will have to change way how your external dependencies/apps load configuration.
You have some information in this post also
PSQL Notify
Postgrex has support for it https://hexdocs.pm/postgrex/Postgrex.Notifications.html It depends on your use case, you can use this with combination of some cache logic. For example Cachex
But combination of running application configuration with dynamic database data changes can be hight way to hell ( I don’t think it will be so good as this song)
