Persistence

[Marc Wachowitz]

Brian Spilsbury <zhivago@iglou.com> wrote:
> Personally I'd vote for a transparent POS, transparent to the point
> where the disk _is_ memory, and we're just using ram for cache,
> then it should be relatively easy to add in persistence of execution.

Please remember that in many practical cases, there are important
semantic differences between having something in memory and having
it on disk. Think of a multi-user database with concurrent nested
and independent transactions, where after immediate hardware crash
(where the disk is still usable), the data on the disk must contain
every committed transaction, and restart must back out everything
else. Assume that this must be possible in a system operating near
the limits of the disk's io performance. You might not worry much
about a system crash while you're editing your source code in memory,
but there are systems where changes are more expensive, and where
changes have non-reversible real-world consequences and commits do
occur with a much higher frequency.

-- Marc Wachowitz <mw@ipx2.rz.uni-mannheim.de>