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Re: snmpconf PM MIB Issue #9




>>>>> Wes Hardaker writes:

Wes> I'm not convinced that forcing this upon the implementer is a
Wes> "good thing".  It's entirely possible that some implementations
Wes> will only be able to write immediately, and others will not be
Wes> able to write until some time X later.

Which means that management applications can never know whether a
configuration change has been committed to stable storage. From a
management application perspective, this is unworkable. (And all the
CLIs I have seen sofar have a "write config now" button. So why is
that too hard to put into an SNMP agent?)

Wes> I fail to see what the problem is with the existing storage type
Wes> mechanisms.  If one box must write everything nonVolatile at once
Wes> and another one may not, then it is sort of implementation
Wes> specific as to what saving methodology is used.

The problem is that management applications have no clue when a
configuration change is reflected in stable storage and hence they
can't seriously make any assumptions that a row which is "nonVolatile"
is still there after a device reboot/crash. I know one implementation
which writes to stable storage when the agent exits (which won't work
if the agent or the system crashes). I know other implementations
which delay writes to speed up the processing of SNMP set
operations. Again, there is a time window where changes to
"nonVolatile" rows might get lost.

The proposal adds explicit write buttons so when a management
application touches the button, it will be sure that the configuration
in stable storage is updated. This does not reduce your freedom to not
implement such a write button and to continue with the old behaviour
where things are written to stable storage whenever the implementor
things it is a good time to do so.

In fact, the write buttons would be an _additional_ explicit mechanism
to help management applications that want to know when configuration
changes are saved in stable storage.

/js

-- 
Juergen Schoenwaelder      Technical University Braunschweig
<schoenw@ibr.cs.tu-bs.de>  Dept. Operating Systems & Computer Networks
Phone: +49 531 391 3289    Bueltenweg 74/75, 38106 Braunschweig, Germany
Fax:   +49 531 391 5936    <URL:http://www.ibr.cs.tu-bs.de/~schoenw/>