Created attachment 113531 [details] persistence test that should work but doesn't e.g. see https://bugs.webkit.org/show_bug.cgi?id=71313 and attached test which doesn't quite work.
https://bugs.webkit.org/show_bug.cgi?id=83074 enables this - once all connections are closed the backing store is actually released. That patch includes a basic persistence test for one issue discovered during implementation, but it can be the basis of this TODO item.