[AFS3-std] Re: abort packet format

[Tom Keiser]

On Wed, Mar 9, 2011 at 1:23 PM, Jeffrey Altman
<jaltman@your-file-system.com> wrote:
> While I have no objections to discussions regarding extending the RX
> abort packet format, I agree with Jeffrey Hutzelman that we need to
> understand what we intend to do with it. =A0I do not believe that
> extending the packet format to describe "throttling" is a good idea.
>

I think I agree, although for slightly nuanced reasons: I'm concerned
that we will implement dynamic behavior on the client that is
ostensibly correct, yet ultimately fails by virtue of being somewhat
naive.  We need to take careful note of the fact that a big
distributed system is inherently a dynamics problem, and thus
simplistic control solutions tend to cause oscillation.  If we're
going to do this, we need to think long and hard about how to approach
distributed throttling from the perspective of control theory (e.g.,
is throttling information necessary and sufficient for clients to make
good decisions?).  Does anyone have the time and patience to start
thinking about distributed systems control, load balancing, and
throttling in terms of phase space and systems of differential
equations? ;)

That being said, I guess I'm not entirely opposed to encoding such
information (in a very generic sense) on the wire, as I do think
server-side throttling is a common-enough technique that most any
non-trivial RPC server must implement it in some form or another.
However, I think the I-D would need to explicitly warn implementors
about the perils of using this information for purposes of
implementing dynamic client behavior...

Cheers,

-Tom