[jboss-jira] [JBoss JIRA] Commented: (JGRP-1331) Digest: remove low seqno

[Bela Ban (JIRA)]

    [ https://issues.jboss.org/browse/JGRP-1331?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12621539#comment-12621539 ] 

Bela Ban commented on JGRP-1331:
--------------------------------

The same principle can be applied to Digests in memory: when we get a byte buffer
| COMPRESSED_SHORT_BYTE | 100000 | 20000 | -1 |
, we can make Digest simply wrap the byte buffer and the methods such as getHighestReceived() would operate on the byte buffer !

The method knows (by consulting the options flag) that we have 8 bytes (a long) for the low seqno, a short (2 bytes) for the highest_delivered and 1 byte for the higest_delivered. It has to read the first byte (options flag), the long (low) and then the next 2 bytes (short), to construct the offset which is added to low to arrive at the highest_received seqno.

This way, we can save even more memory.

> Digest: remove low seqno
> ------------------------
>
>                 Key: JGRP-1331
>                 URL: https://issues.jboss.org/browse/JGRP-1331
>             Project: JGroups
>          Issue Type: Task
>            Reporter: Bela Ban
>            Assignee: Bela Ban
>            Priority: Minor
>             Fix For: 3.1
>
>
> We don't need Digest.Entry.low_seqno for NakReceiverWindow anymore. We only need it for the Retransmitter implementations. If we can remove that last dependency, e.g. by storing the last seqno removed from a retransmitter, we can remove low_seqno from a digest. This is significant, for example if we have 100 nodes, a digest includes 300 longs:(low+highest_received+highest_delivered) * 100. If we remove low_seqno, we only have 200 longs. (These will still be further compressed in a different JIRA).
> This is important for large clusters, to reduce the size of STABLE messages and views.

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