[jboss-jira] [JBoss JIRA] (JGRP-1821) SEQUENCER2: new impl of total order protocol

SEQUENCER2: new impl of total order protocol -------------------------------------------- Key: JGRP-1821 URL: https://issues.jboss.org/browse/JGRP-1821 Project: JGroups Issue Type: Feature Request Reporter: Bela Ban Assignee: Bela Ban Fix For: 3.5 When in {{SEQUENCER}} a member P wants to send a multicast message M, it unicasts it to the coordinator, who multicasts it on behalf of P. The new impl {{SEQUENCER2}} is different: * P asks the coord for a seqno * The coord responds with a (monotonically increasing) seqno * P multicasts M with that seqno * Everyone uses one global {{Table}} to deliver messages and weed out duplicates Advantages: # A sender sends messages itself, so the sequencer doesn't need to do sending (and potential retransmissions) # Compared to {{SEQUENCER}}, the data is only sent and marshalled once (better for large messages) # A sender grabs entire ranges of seqnos, so this should be efficient The edge case handling though requires some work, e.g. * A member B crashes after having received a seqno (e.g. 4) ** The sequencer will give out 5 next, but since nobody received 4, all subsequent messages will get stuck, waiting for 4 * The sequencer (coord) dies or leaves ** The next-in-line probably needs to run some reconciliation protocol, asking all members for their highest received seqnos ** Messages like 4 would get marked as dummy, removed from table and dropped