[Spread-users] Circular token over spread: 2 seconds lap time?

[Yair Amir]

Hi,

Just to contribute a bit:

Jonathan> The Hurry timeout is how long the 'leader' of the token ring will hold
Jonathan> then token when NO other daemon wants the token. To emphasize this, if at 
Jonathan> least some of the daemons have messages to send, then the token will keep 
Jonathan> circling with no additional delay (i.e. hurry timeout has no effect). If 
Jonathan> the token circles several times around the ring and NO messages are sent 
Jonathan> (the counters do not increase) then the leader will grab the token and 
Jonathan> hold it for Hurry_timeout seconds. Then it will send it around the ring 
Jonathan> again in case daemons now have messages. 

Spread is a bit smarter then that - if the token is held by the
representative (leader) then the other daemons know this (they
calculate the same calculation). If any of them has a message to send,
it will immediately ask the representative to start circulating the
token. So - no one has to wait for a Hurry timeout if they have
something to send. At least this is what was programmed to the code in
the past.

It seems that it is possible that for some reason, this mechanism of
hurrying the token (hence the name) does not work for at least some of
the people on the list. This is worth further investigation, but it
will have to be someone else doing it, or will wait for several weeks
before I can do it myself (there is a vacation in my future and the
future starts tomorrow :)

Jonathan> So if your daemons are always busy the hurry timeout should not effect 
Jonathan> them. If you have a "light" load (a fwe messages per second per daemon) 
Jonathan> then the hurry timeout will increase the latency per message, but will 
Jonathan> avoid the token circling as fast as possible around the ring wasting 
Jonathan> bandwidth. 

So - as per the comment above, this actually should not be the case -
the increase due to holding the token should be no more than a couple
milliseconds once any one has something to send.

Cheers,

       :) Yair.