[jboss-jira] [JBoss JIRA] Commented: (JGRP-952) MERGE: UNICAST can lose messages on merging

MERGE: UNICAST can lose messages on merging ------------------------------------------- Key: JGRP-952 URL: https://jira.jboss.org/jira/browse/JGRP-952 Project: JGroups Issue Type: Bug Reporter: Bela Ban Assignee: Bela Ban Fix For: 2.6.10, 2.8 The following use case loses messages: - A sends #5 to B - B expects #4 from A, but adds #5 and acks it - A receives the ack(#5) and removes #5 from its sender window - Now there is a partition such that B trashes its connection window form A, but A keeps its window for B (A: {A,B}, B: {B}) - The partition heals and A sends #6 to B - B asks A for its lowest seqno, A resends #4 (with a conn_id) - B creates a receiver window for A with seqno=#4 - A resends #6 - B adds #6 to its window, but doesn't deliver it because it is missing #5 --> However, A will NEVER resend #5 because the ack(#5) from B removed #5 from A's sender window ! ==> Possible SOLUTION: when A gets the SEND_FIRST_SEQNO and there are (unacked) messages in A's sender window, and they are not in order, then A will trash its connection window and copy the pending messages into the new window (with new seqnos !) before sending #1 (with conn_id) ==> This solution might lose the original message #5, but that's better than B never being able to deliver any messages anymore !