[jboss-jira] [JBoss JIRA] (JGRP-1539) NAKACK2: xmit_interval sometimes triggers unneeded retransmissions

NAKACK2: xmit_interval sometimes triggers unneeded retransmissions ------------------------------------------------------------------ Key: JGRP-1539 URL: https://issues.jboss.org/browse/JGRP-1539 Project: JGroups Issue Type: Enhancement Reporter: Bela Ban Assignee: Bela Ban Fix For: 3.3 In NAKACK2 (and UNICAST2 as well), a timer task kicks in every xmit_interval milliseconds. If we just added a message out of order, then the retransmit task might send a spurious retransmission message. Example: - Messages 1,2,3,4,5 are received at time T0 (in ms) - At time T1000, message 20 is received - At time T1001, the retransmit task kicks in and asks the sender for retransmission of messages [6-19] - At time T1009, messages 6-19 are received Problem: the out-of-order message 20 was received just before the retransmit task kicked in. Has the task waited for another 9 ms (until time T1009), the retransmission would not have been necessary. The underlying cause is that the retransmit tasks handles recently added gaps the same as gaps added before xmit_interval, as we don't maintain a timestamp for added messages. Another reason is also that the message bundler on the sender side might send messages in random order (see link below). SOLUTION: Investigate how to change the retransmission task such that it excludes gaps created within the last xmit_interval ms.