[jira] [Commented] (HELIX-543) Single partition unnecessarily moved

["Tom Widmer (JIRA)" <ji...@apache.org>]

    [ https://issues.apache.org/jira/browse/HELIX-543?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14204742#comment-14204742 ] 

Tom Widmer commented on HELIX-543:
----------------------------------

Pull request at https://reviews.apache.org/r/27808/

> Single partition unnecessarily moved
> ------------------------------------
>
>                 Key: HELIX-543
>                 URL: https://issues.apache.org/jira/browse/HELIX-543
>             Project: Apache Helix
>          Issue Type: Bug
>          Components: helix-core
>    Affects Versions: 0.7.1, 0.6.4
>            Reporter: Tom Widmer
>            Priority: Minor
>
> (Copied from mailing list)
> I have some resources that I use with the OnlineOffine state but which only have a single partition at the moment (essentially, Helix is just giving me a simple leader election to decide who controls the resource - I don’t care which participant has it, as long as only one does). However, with full auto rebalance, I find that the ‘first’ instance (alphabetically I think) always gets the resource when it’s up. So if I take down the first node so the partition transfers to the 2nd node, then bring back up the 1st node, the resource transfers back unnecessarily.
> Note that this issue also affects multi-partition resources, it’s just a bit less noticeable (it means that with 3 nodes and 4 partitions, say, the partitions are always allocated 2, 1, 1, so if you have node 1 down and hence 0, 2, 2, and then bring up node 1, it unnecessarily moves 2 partitions to make 2, 1, 1 rather than the minimum move to achieve ‘balance’ which would be to move 1 partition from instance 2 or 3 back to instance 1.
> I can see the code in question in AutoRebalanceStrategy.typedComputePartitionAssignment, where the distRemainder is allocated to the first nodes alphabetically, so that the capacity of all nodes is not equal.
> The proposed solution is to sort the nodes by the number of partitions they already have assigned, which should mean that those nodes are assigned the higher capacity and the problem goes away.



--
This message was sent by Atlassian JIRA
(v6.3.4#6332)