I'm trying to understand how data storage works in this application.
- How is data stored in the database?
- How is data stored locally on the device?
- If the database connection is unavailable, is the data stored locally? If so, where and how is it synchronized once the connection is restored?
- When the database connection is available, is the data still stored locally (for caching or offline support), or is it written directly to the database?
- Can someone explain the overall data flow for both online and offline scenarios?
What do you mean by "data"? are you talking about tag history? Are you talking about custom table data, audit log data, alarm history (journal) data? Or all of the above?
The store and forward system will be the main system employed for all of these, except custom table data is up to you. There are scripting functions that can either use the S+F system or not, depending on the circumstance. If you need the query you run to return something to continue the script, you won't be able to use the s+f system for example. But generally you would opt to go through it for the obvious benefit it gives
To clarify on this point, there is no single “method” to store data in Ignition. There are many valid approaches.
This is one of the many benefits of Ignition over the competition (which may only have a single method of storing data).
I highly suggest you view some of the database related videos at Inductive University.