[jira] [Commented] (HBASE-3679) Provide cost information associated with moving region(s)

["Ted Yu (JIRA)" <ji...@apache.org>]

    [ https://issues.apache.org/jira/browse/HBASE-3679?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13009469#comment-13009469 ] 

Ted Yu commented on HBASE-3679:
-------------------------------

>From Jonathan:
One of the hardest parts of load balancing based on request count and other dynamic/transient measures is that you can get some pretty pathological conditions where you are always moving stuff around.

To guard against it, I think we'll need to move to more of a cost-based algorithm that is taking not just the difference in request counts into account but also a baseline "cost" of moving a region.  The cost difference in load between two unbalanced servers would have to outweigh the cost associated with moving a region.  As you say, looking at the number of live operations to a given region could contribute to the cost of moving that region, but the best measure for that is probably just looking at request count (it's all requests that incur a cost, not just active scanners).

> Provide cost information associated with moving region(s)
> ---------------------------------------------------------
>
>                 Key: HBASE-3679
>                 URL: https://issues.apache.org/jira/browse/HBASE-3679
>             Project: HBase
>          Issue Type: Improvement
>            Reporter: Ted Yu
>
> In order for load balancer to make better decision, we need to establish cost model for moving region(s).
> One factor would be the number of active scanners on a particular region.
> This count is easy to maintain at HRegion level. instantiateInternalScanner() can increment the counter and RegionScanner.close() would decrement the count.

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