[jboss-jira] [JBoss JIRA] (JGRP-1391) Compress MergeViews

[Bela Ban (JIRA)]

     [ https://issues.jboss.org/browse/JGRP-1391?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel ]

Bela Ban resolved JGRP-1391.
----------------------------

    Resolution: Done

    
> Compress MergeViews
> -------------------
>
>                 Key: JGRP-1391
>                 URL: https://issues.jboss.org/browse/JGRP-1391
>             Project: JGroups
>          Issue Type: Enhancement
>            Reporter: Bela Ban
>            Assignee: Bela Ban
>             Fix For: 3.4
>
>
> The 'subgroups' field of MergeView is a list of Views, referring to the subclusters that formed the new view.
> Each View in that list contains (1) the creator of the view, (2) an ID and (3) a list of member addresses.
> Both (1) and (3) are present in the new MergeView, so, to save memory and message sizes, 'subgroups' could be compressed: (1) and (3) could be indices into View's 'members' field. 
> Example: if we have MergeView A|22=\{A,B,C,D,E,X,Y,Z\}, subgroups=A|21=\{A,B,C\}, D|19=\{D,E\}, X|20=\{X,Y,Z\},
> then 'subgroups' can be compressed as follows:
> subgroups=0|21=\{0,1,2\}, 3|19=\{3,4\}, 5|20=\{5,6,7\}
> This is possible because the indices never change, as the contents of Views and MergeViews are static, e.g. we can never add or remove a member: to do this, a new View/MergeView would be created.
> Substituting addresses with indices (shorts, possibly using variable-bit encoding) reduces the memory footprint of a view, and the size of a serialized view on the wire.
> Getting the subgroups field, e.g. using method getSubgroups() would synthesize the List<View> just-in-time.

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