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https://issues.apache.org/jira/browse/HBASE-5510?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13221094#comment-13221094
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ramkrishna.s.vasudevan commented on HBASE-5510:
-----------------------------------------------
@Ted
The rationale is like,
I have set of regions S1...Sn and R1...Rn...In this i expect S1-R1, S2-R2 ...to
be colocated in the same RS.
S1...Sn are balanced by one LB.
There is a custom LB which will balance R1..Rn. Now this LB should get the
assignment done by first LB and based on that it will assign R1..Rn. Finally
ensuring the colocation.
Am i clear Ted?
> Change in LB.randomAssignment(List<ServerName> servers) API
> -----------------------------------------------------------
>
> Key: HBASE-5510
> URL: https://issues.apache.org/jira/browse/HBASE-5510
> Project: HBase
> Issue Type: Improvement
> Affects Versions: 0.92.0
> Reporter: Anoop Sam John
> Assignee: ramkrishna.s.vasudevan
>
> In LB there is randomAssignment(List<ServerName servers>) API which will be
> used by AM to assign
> a region from a down RS. [This will be also used in other cases like call to
> assign() API from client]
> I feel it would be better to pass the HRegionInfo also into this method.
> When the LB making a choice for a region
> assignment, when one RS is down, it would be nice that the LB knows for
> which region it is doing this server selection.
> +Scenario+
> While one RS down, we wanted the regions to get moved to other RSs but a set
> of regions stay together. We are having custom load balancer but with the
> current way of LB interface this is not possible. Another way is I can allow
> a random assignment of the regions at the RS down time. Later with a cluster
> balance I can balance the regions as I need. But this might make regions
> assign 1st to one RS and then again move to another. Also for some time
> period my business use case can not get satisfied.
> Also I have seen some issue in JIRA which speaks about making sure that Root
> and META regions always sit in some specific RSs. With the current LB API
> this wont be possible in future.
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