[jboss-jira] [JBoss JIRA] (JGRP-1317) Compress Digest and MutableDigest

[Bela Ban (JIRA)]

    [ https://issues.jboss.org/browse/JGRP-1317?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12802161#comment-12802161 ] 

Bela Ban commented on JGRP-1317:
--------------------------------

Another alternative is to revert Digest to containing a membership list (Address[]) and the corresponding seqnos (long[]). This is essentially what we had in the beginning.

However, *if View's membership list was changed from an ArrayList<Address> to an array (Address[])*, then we could do the following when unmarshalling a ref digest:
* Read the View
* Read the seqno[] array of the digest
* Point the Address[] array of digest to the Address[] array of view, so we have the Address[] aray in memory *only once*

Protocols which need a view-id could simply ship the view-id, e.g. STABLE.
                
> Compress Digest and MutableDigest
> ---------------------------------
>
>                 Key: JGRP-1317
>                 URL: https://issues.jboss.org/browse/JGRP-1317
>             Project: JGroups
>          Issue Type: Feature Request
>            Reporter: Bela Ban
>            Assignee: Bela Ban
>             Fix For: 3.4
>
>
> For large clusters, STABLE messages are quite large, and should be compressed to be sent over the wire. 
> STABLE messages are sent between members in the same view, so we could only send the ViewId + highest_delivered/highest_received seqnos.
> Everybody who receives a STABLE message grabs the View associated with the ViewId (should be the current view !) and creates a Digest based on the View and the long[] array.
> Further optimization:
> - Canonicalize digests: if everyone has (14) 20, 22, then we could write it once, give it an ID of (say) 1 and then only refer to 1 again if we encounter the same digest. Actually, as a matter of fact, most of the digests would be the same, so this optimization could have a big effect !

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