[jboss-jira] [JBoss JIRA] Resolved: (JGRP-966) UNICAST: multiple SEND_FIRST_SEQNO messages cause message loss

[Bela Ban (JIRA)]

     [ https://jira.jboss.org/jira/browse/JGRP-966?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel ]

Bela Ban resolved JGRP-966.
---------------------------

    Resolution: Done


fixed according to suggested solution

> UNICAST: multiple SEND_FIRST_SEQNO messages cause message loss
> --------------------------------------------------------------
>
>                 Key: JGRP-966
>                 URL: https://jira.jboss.org/jira/browse/JGRP-966
>             Project: JGroups
>          Issue Type: Bug
>            Reporter: Bela Ban
>            Assignee: Bela Ban
>             Fix For: 2.6.10.merge, 2.8
>
>
> If we have A and B:
> A: 5 6 7 8 9 and 
> B: -
> - A sends #5 - # 9 to B, then B will send a SEND_FIRST_SEQNO to A per message for a total of 5
> - A resends #5 with a conn-id of (say) 322649
> - B creates the receiver window for A with conn-id=322649 and adds #5, then removes it and acks #5
> - A receives an ack for #5 and removes #5 from it sender window
> - A then receives the next (stale) SEND_FIRST_SEQNO request
> - A now resends #6 with a conn-id=322649
> ---> B drops #6 (and all subsequent messages) with conn-id=322649 !
> ==> The simple solution is to not drop messages with a conn-id if the receiver window already exists *and* the conn-ids match
> Potential issue: what if we re-send #6 with conn-id=322649 *before* #5 with conn-id=322649 ?
> - A message on the sender side is only removed if it received an ACK from the receiver
> - Reception of an ACK means the receiver window was created
> - When we receive ACK(5), that means we created a receiver window  on B with conn-id=322649 and added #5
> - Therefore the re-sending of #6 with conn-id=322649 will *never* happen before the receiver window on B is created for #5 and conn-id=322649 !

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