Hi all,
 
The topic of message files and their recovery after a system
failure was raised recently.  It occurred to me to ask:
 
   What if MPE is changed to guarantee that message files are never
   corrupted by a system failure, at the cost of always throwing away
   pending messages if the file was open when the system crashed?
 
BTW, I haven't personally encountered corrupted message files on
MPE/iX 5.0, although I've heard one report about that happening.
I mention this in advance, in case the MPE lab says "hey, there shouldn't
be any corruption now!", in which case my proposal is changed to: never mind.
 
I think the following would suffice:
 
   - when a message file is opened, flag it as "needs cleaning".
     Post the flag to disk.  (Note: opening for COPY mode wouldn't
     set the flag...but read or write mode would.)
 
   - at system bootup (or, when the message file is first opened after
     a system failure), if the "needs cleaning" flag is on,
     the message file would be emptied and guaranteed to be "clean".
 
This would prevent the problems that a lot of us have encountered
with message files.
 
What do we lose?  The possibility of having useful records in the
message files.
 
What do we gain?  Robustness, safety, and a guaranteed startup condition.
 
What is the implementation cost?  Probably low.
 
What do people think?
 
Stan Sieler                                          [log in to unmask]
                                     http://www.allegro.com/sieler.html