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From "Anoop Sam John (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (HBASE-18946) Stochastic load balancer assigns replica regions to the same RS
Date Tue, 05 Dec 2017 10:31:00 GMT

    [ https://issues.apache.org/jira/browse/HBASE-18946?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16278359#comment-16278359
] 

Anoop Sam John commented on HBASE-18946:
----------------------------------------

Before the patch, the regions are created and the AssignProcedure for them. There is no target
server in the procedure and we will contact the LB (RoundRobin or RetainAssign calls).   Now
say when a table is created, then itself the target servers for each of the regions are selected
NOT contacting the LB but much earlier by AM. So the LB is not been asked at all.. What if
the cluster is having the RS group feature and using that LB?  There is all chance that the
regions go to some servers where the admin dont want this table to go!  I think we can not
do this way.

> Stochastic load balancer assigns replica regions to the same RS
> ---------------------------------------------------------------
>
>                 Key: HBASE-18946
>                 URL: https://issues.apache.org/jira/browse/HBASE-18946
>             Project: HBase
>          Issue Type: Bug
>    Affects Versions: 2.0.0-alpha-3
>            Reporter: ramkrishna.s.vasudevan
>            Assignee: ramkrishna.s.vasudevan
>             Fix For: 2.0.0-beta-1
>
>         Attachments: HBASE-18946.patch, HBASE-18946.patch, HBASE-18946_2.patch, HBASE-18946_2.patch,
HBASE-18946_simple_7.patch, HBASE-18946_simple_8.patch, TestRegionReplicasWithRestartScenarios.java
>
>
> Trying out region replica and its assignment I can see that some times the default LB
Stocahstic load balancer assigns replica regions to the same RS. This happens when we have
3 RS checked in and we have a table with 3 replicas. When a RS goes down then the replicas
being assigned to same RS is acceptable but the case when we have enough RS to assign this
behaviour is undesirable and does not solve the purpose of replicas. 
> [~huaxiang] and [~enis]. 



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