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: 3.5.1, 3.6 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-FIRST-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 previous 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