What is the core database system used by QGIS?
When you launch an existing project that has multiple .shp files (with associated .dbf tables), is the core db system used to convert that data to its own internal format as the project loads?
How about joining a simple CSV; does the core database have that import functionality, or does a Python script run independent of the core database, perform a conversion on the fly, then the core database takes the data from that script?
Once you have a project fully loaded, including a .shp file plus a .dbf, plus another CSV joined, are all the data in one common database system, so performance should be crisp and brisk? Or, does the system read in only the data needed to render the scale and scrolling you are at on the canvas, and continually re read that external CSV join as you zoom and pan around?
Suspect PostgreSQL at the core, or SQLite at the core? (So, any bug issues with those db systems will show through to QGIS?)
Are there any notes on import/export to the core database used, particularly any "rough spots" (CSV joins for instance, appears to trip many new users up.) Are those QGIS issues or the underlying db issue?
I see PosgreSQL is really Ingress (which lacked SQL), with nicely compliant SQL finally added (evolving to Post Ingress), with some object features added (including possibly spacial objects like point, line and poly)?
If PostgreSQL lies at the heart of QGIS, I'd expect performance "rotating" / manipulating relational data to be outstanding? (Ingress on pure relational data in its original form was outstanding as I recall... Do the "add ons" later on come at a cost of the core relational performance?