[jboss-jira] [JBoss JIRA] Updated: (JGRP-1053) UNICAST: set retransmission timeout based on actual retransmission times

[Bela Ban (JIRA)]

     [ https://jira.jboss.org/browse/JGRP-1053?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel ]

Bela Ban updated JGRP-1053:
---------------------------

    Fix Version/s: 3.0
                       (was: 2.11)


Investigate in conjunction with dynamically changing credits in flow control

> UNICAST: set retransmission timeout based on actual retransmission times
> ------------------------------------------------------------------------
>
>                 Key: JGRP-1053
>                 URL: https://jira.jboss.org/browse/JGRP-1053
>             Project: JGroups
>          Issue Type: Feature Request
>            Reporter: Bela Ban
>            Assignee: Bela Ban
>             Fix For: 3.0
>
>
> UNICAST needs to compute a rolling average of retransmission times, per sender (AckSenderWindow).
> The retransmission timeout per sender can then be set based on the actual average retransmission times. The advantage is that we throttle retransmission when we have a lot of message loss, and speed it up again when there are no message drops.
> The function to set the timeout should always compute the new timeot value based on (1) the old value times a decay factor and (2) a new value.
> The average should go up relatively quickly if the actual retransmission values go up, but come down slowly when the actual values go down.
> A potential function is shown below:
>     static final double SLOW_DECAY_FACTOR=0.9, FAST_DECAY_FACTOR=0.7;
>     static final double FAST_UP= 1 / FAST_DECAY_FACTOR, SLOW_UP= 1 / SLOW_DECAY_FACTOR;
>     static final double SAFETY_BUFFER=0.3;
>     static double avg=200;
>     public static void main(String[] args) {
>         final long[] times={200,200,400,400,500,500,500,500,500,100,100,100,100,100,100,100,100,100,100,100,100,100};
>         // final long[] times={200,200,200,200,200,200,200,200,200,200,200};
>         for(Long val: times) {
>             double result=avg(val);
>             System.out.println(val + ": " + result);
>         }
>     }
>     private static double avg(long val) {
>         double decay, up;
>         if(val > avg) {
>             decay=FAST_DECAY_FACTOR;
>             up=FAST_UP;
>         }
>         else {
>             decay=SLOW_DECAY_FACTOR;
>             up=SLOW_UP;
>         }
>         double old_val=avg * decay;
>         double result=(old_val + val * up) / 2;
>         avg=result;
>         return result * (1 + SAFETY_BUFFER);
>     }

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