Re: libefs

[Dietmar Maurer <dm vlsivie tuwien ac at>]

David Orme wrote:
> Since we're reimplementing this, we have the opportunity to fix this
> oversight by providing a separate process that manages reading/writing open
> files on behalf of the client applications.  If a client application crashes
> in the middle of a save, the transaction is rolled back and the user loses
> just the work from the current session, not the entire file.

You can never get an inconsistent database with the current
implementation of libefs (due to client crashes), because I don't
overwrite the last version. Keeping the last version is the only way to
implement this behaviour. This also mean that it is very difficult to
"compact" the filesystem - because if I overwrite data I can't do a
rollback. The easiest way to "compact" the filesystem is to copy the
whole thing to a new location and then make a (atomic) rename.

> While I'm on the topic of file systems within a file, we also need the
> ability to mount external directories within our "file system within a
> file".  Another MS Access problem is that it is hard to share an application
> without sharing all of your data as well since the forms used to implement
> the application are stored in the same file as the data.

Please can you explain that more detailed.