Re: Keep-Alive Notes
Dave Kristol (dmk@allegra.att.com)
Thu, 12 Oct 95 12:27:27 EDT
Henrik Frystyk Nielsen <frystyk@w3.org> wrote:
> [...]
> [argues that the relative values of timeouts can be used by the client
to order requests]
> Therefore at least the timeout does convey useful information. As HTTP is
> "measured in seconds" I don't think that roundtrip delays will have a
> significant influence in this game.
I'm not sure I follow your point. When the network is slow and/or
congested, the delays can be that bad, I think.
Consider, also, the role of intermediaries. What timeout value should a
proxy pass along? Suppose we have the pipeline
C -> P -> S (client/proxy/server)
and the server says timeout=5. What does the proxy say to the client,
assuming it keeps the whole pipeline open? Timeout=5? The client then
thinks it has five seconds to respond. But that five seconds applies
only to the C-P connection. Taking into consideration the proxy's
processing time and the propagation times S-P and P-C, that's a
misleading number. So, should P say timeout=N for some N<5? Certainly
it doesn't want to pick N>5.
(Roy, will you state rules for what an intermediary should say w.r.t.
timeout?)
Henryk argues that the relative values can be used to order requests.
But suppose C gets one response with timeout=5 and another with
timeout=6. Suppose the latter has come through a connection that
involves several proxies. The value of 6 may be well-degraded to the
point where a failure to respond on that channel first will render the
keep-alive useless.
I find it hard to imagine the timeout information to be useful.
Dave Kristol