[jboss-jira] [JBoss JIRA] Commented: (JGRP-825) Message: add a flag to discard own multicast

[Bela Ban (JIRA)]

    [ https://jira.jboss.org/jira/browse/JGRP-825?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12434654#action_12434654 ] 

Bela Ban commented on JGRP-825:
-------------------------------

This requires quite a number of changes:
- TP.receive() needs to drop messages with the DISCARD_OWN_MCASTS flag
- NAKACK.send() needs to remove a DISCARD-tagged message as soon as added (overhead if not tagged at all)
- NAKACK.up() needs to check if the message is tagged and discard it if so (and we sent it)
- FC does NOT get a tagged message, therefore it won't decrement its received credits and the sender will block because it doesn't get replenishments. This code can be changed to send credits on down() (if sender == dest), but this is a kludge

All in all, perf doesn't get better than before, and I tend to cancel this feature...

> Message: add a flag to discard own multicast
> --------------------------------------------
>
>                 Key: JGRP-825
>                 URL: https://jira.jboss.org/jira/browse/JGRP-825
>             Project: JGroups
>          Issue Type: Feature Request
>            Reporter: Bela Ban
>            Assignee: Bela Ban
>             Fix For: 2.7
>
>
> If we have a group consisting of members {A,B,C} and A wants to multicast to the group, it will receive its own message too. To avoid this, A can set option LOCAL on its channel to false, meaning that all messages sent by A will get discarded by A's channel.
> The problem here is that those messages need to get handled nevertheless (e.g. by NAKACK, including retransmissions), all the way up the stack, until they hit the channel - only to be discarded there. This is a waste of resources (CPU and memory).
> A solution is to discard the multicast at the transport level. If a message has a flag LOCAL set to false, then TP discards it if
> - the message is a multicast message and
> - the sender of the message is the local member

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