[jboss-jira] [JBoss JIRA] (JGRP-1874) UNICAST3/UNICAST2: reduce traffic caused by GET-FIRST-SEQNO

[Bela Ban (JIRA)]

Bela Ban created JGRP-1874:
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             Summary: UNICAST3/UNICAST2: reduce traffic caused by GET-FIRST-SEQNO
                 Key: JGRP-1874
                 URL: https://issues.jboss.org/browse/JGRP-1874
             Project: JGroups
          Issue Type: Enhancement
      Security Level: Public (Everyone can see)
            Reporter: Bela Ban
            Assignee: Bela Ban
             Fix For: 3.5


When we have sender A and receiver B, and B closes its connection unilaterally (see JGRP-1873), then a {{GET-FIRST-SEQNO}} will be sent from B to A when A's next message is received. This can potentially generate a lot of traffic.
Example:
# B has no entry for A in its recv-table
# A has {{B:: 100 | 1000}}, so only message {{A::100}} has been acked by B ({{STABLE}} or {{ACK}} message
# If B now gets {{A::560}}, it sends a {{GET-FIRST-SEQNO(560)}} to A
#* As a matter of fact, for any message from A that not marked as {{first}}, B will send a {{GET-FIRS-SEQNO message}}: too much traffic
# A now sends messages {{A::101}} - {{A::560}} to B
#* This is also not needed: too much traffic

h5. Solution to reduce traffic
* Receiver: add timestamp to recv-table entries which drops {{GET-FIRST-SEQNO}} messages sent sooner than N ms after the last one
** So rather than sending 1000 {{GET-FIRST-SEQNO}} messages to A when receiving 1000 unicasts from A not marked as {{first}}, we might only send a _single message_
* Sender: when a {{GET-FIRST-SEQNO(560)}}  message is received from B, only send the lowest sent (101) and the highest sent (560) back to B
** B will then retransmit all missing messages in that range
** For {{UNICAST3}}, we can only send the lowest sent message (101) as it will retransmit {{A::1000}} anyway and therefore trigger retransmission



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