[mnet-devel] Re: [mnet-cvs]calculate timeouts according to size of sent message

[Zooko O'Whielacronx]

-def calculate_timeout(mu, sigma):
-    return mu + 3*sigma
+def calculate_timeout(mu, sigma, size=500):
+    return (mu*size/500) + sigma)

> yes, but initiating messages can be 250 bytes or very big ("put block", 
> "message for you").

"put block" should be handled fine by the traditional statistical timeout, since 
"put block" messages are always the same size.  You're right about "message for 
you".

> This was why it was introduced in 0.7. Should at least help in these 
> cases, and not hurt anywhere else...

Well, I'm not so sure that it won't hurt.  The new version doesn't increase for 
variance as much as the old, which means that we'll get more timeouts on 
messages which vary more.  For example, "are there messages" varies a great deal 
due to the size of the response, and so this patch *might* cause "preferred 
relay server churn", where there usually isn't a message when you ask "are there 
messages", so the mu is small, but then whenever there *is* a message you get a 
timeout and start to prefer a new relayer.  Hopefully that won't happen because 
of the late responses and the "stick with current relayer" handicapper, but 
I'm not perfectly sure it won't cause that kind of problem either in relayer or 
somewhere else.

On the other hand, I don't think it helps much -- changing calculate_timeout() 
is probably not really needed at this point, now that we have these various 
recent fixes, especially the TCP linger close patch.  The only message type 
where including the size of the message should make a big difference is "message 
for you", and it doesn't make that much difference if a "message for you" times 
out.  I *think* the worst that can happen is the underlying TCP connection is 
closed and a new one re-opened.

I didn't really like its addition to v0.7, for the same reasons.  (That was 
Tschechow's idea in v0.7.)

Regards,

Zooko



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