Persistence

[Martin Schaffner]

On Thu, 27 Oct 2005 22:08:39 -0400, Jonathan S. Shapiro wrote:

> As to cost, yes, I am afraid that EROS-style persistence is
> significantly more efficient than conventional file systems, and we
> would face a definite design burden finding interesting uses for the
> newly available disk bandwidth.

If I understand correctly, then what persistence does is keep a memory 
dump of everything on disk, so a power outage does not destroy any 
data. This also makes constant "saving" unnecessary. I guess this 
mechanism is related to swapping (the app tells the system which pages 
it will need in the future, the OS pages them in and out, and a power 
failure just means that the app needs to be paged in again). Is this 
true?

If yes, then when one wants to back up a document or transfer it to 
another machine, these memory dumps might not be very useful, as 
traditionally memory dumps are machine-dependent (byte order, 
alignment, absolute pointers) for speed, while file formats are 
designed to be machine-independent. How do editors work in persistent 
systems? Do they also offer a "save" function, or maybe an "export to 
file" function (so that the collaboration of all apps would be 
necessary for a system back-up)? Or is the memory dump 
machine-independant, which means a speed loss and a big burden for 
porting legacy apps?

Thanks,
Martin