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https://issues.apache.org/jira/browse/IGNITE-12133?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16960532#comment-16960532
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Moti Nisenson-Ken commented on IGNITE-12133:
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After looking a bit deeper into it, I think that [~ivan.glukos] is on the right
track. It would make most sense to implement this first as a general mechanism
for broadcasting a message to a set of nodes, before looking into this for
discovery. That way it could be leveraged where it makes sense, and then a
decision could be made whether it makes sense to use as part of discovery or
not when it is stable.
In this case, we'd talk about the initiator (instead of the coordinator), and
the skip list would then start from that the initiator. Since it's general,
there should be efficient ways to support common cases from a message format
perspective. Common cases would likely be things like : when the coordinator is
the initiator, where the set of nodes is all nodes, or the set of nodes are
those nodes having data for a cache, or all baseline topology nodes, etc. For a
random subset of nodes it would require including the nodes to be contacted in
the message of course.
> O(log n) partition exchange
> ---------------------------
>
> Key: IGNITE-12133
> URL: https://issues.apache.org/jira/browse/IGNITE-12133
> Project: Ignite
> Issue Type: Improvement
> Reporter: Moti Nisenson-Ken
> Priority: Major
>
> Currently, partition exchange leverages a ring. This means that
> communications is O\(n) in number of nodes. It also means that if
> non-coordinator nodes hang it can take much longer to successfully resolve
> the topology.
> Instead, why not use something like a skip-list where the coordinator is
> first. The coordinator can notify the first node at each level of the
> skip-list. Each node then notifies all of its "near-neighbours" in the
> skip-list, where node B is a near-neighbour of node-A, if max-level(nodeB) <=
> max-level(nodeA), and nodeB is the first node at its level when traversing
> from nodeA in the direction of nodeB, skipping over nodes C which have
> max-level(C) > max-level(A).
> 1
> 1 . . .3
> 1 3 . . . 5
> 1 . 2 . 3 . 4 . 5 . 6
> In the above 1 would notify 2 and 3, 3 would notify 4 and 5, 2 -> 4, and 4 ->
> 6, and 5 -> 6.
> One can achieve better redundancy by having each node traverse in both
> directions, and having the coordinator also notify the last node in the list
> at each level. This way in the above example if 2 and 3 were both down, 4
> would still get notified from 5 and 6 (in the backwards direction).
>
> The idea is that each individual node has O(log n) nodes to notify - so the
> overall time is reduced. Additionally, we can deal well with at least 1 node
> failure - if one includes the option of processing backwards, 2 consecutive
> node failures can be handled as well. By taking this kind of an approach,
> then the coordinator can basically treat any nodes it didn't receive a
> message from as not-connected, and update the topology as well (disconnecting
> any nodes that it didn't get a notification from). While there are some edge
> cases here (e.g. 2 disconnected nodes, then 1 connected node, then 2
> disconnected nodes - the connected node would be wrongly ejected from the
> topology), these would generally be too rare to need explicit handling for.
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