[jira] [Commented] (IGNITE-12133) O(log n) partition exchange

["Anton Vinogradov (Jira)" <ji...@apache.org>]

    [ https://issues.apache.org/jira/browse/IGNITE-12133?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16920687#comment-16920687 ] 

Anton Vinogradov commented on IGNITE-12133:
-------------------------------------------

[~mnk], 

1) In the case of skip-list approach usage, we will lose discovery message processing order guarantee.

P.s. Not sure we need it at some case :) just an addition.


2) BTW, we already have a discovery implementation based on ZooKeeper. ([https://apacheignite.readme.io/docs/zookeeper-discovery])

Anyway, seems, this optimization will speed-up the ring instead of replacement with a star.

 

Could you start devlist discussion before the implementation?

> 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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