The SQLALCHEMY_DATABASE_URI variable value is picked up by the Flask-AppBuilder manager to create the metadata database for the web app. The metadata database is persisted in ~/.superset/superset.db by default. This can be verified by running sqlite3 in the directory and listing the tables in the database:
shashank@superset:~/.superset$ sqlite3
SQLite version 3.16.2 2017-01-06 16:32:41Enter ".help" for usage hints.Connected to a transient in-memory database.Use ".open FILENAME" to reopen on a persistent database.
sqlite> .open superset.db
sqlite> .tables
ab_permission annotation_layer logs ab_permission_view clusters metrics ab_permission_view_role columns query ab_register_user css_templates saved_query ab_role dashboard_slices slice_user ab_user dashboard_user slices ab_user_role dashboards sql_metrics ab_view_menu datasources...
