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From: Martin Schaffner
Subject: Persistence
Date: Fri, 28 Oct 2005 07:49:18 +0200

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?


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