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https://issues.apache.org/jira/browse/HBASE-18946?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16256922#comment-16256922
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ramkrishna.s.vasudevan commented on HBASE-18946:
------------------------------------------------
Some updates here
-> In roundRobinAssignment the LB does not even care for the replicas and its
assignment. So we need to make it aware of it. It knows that the region has a
replica but it does not check if same replica is being assigned only balancer
knows about it.
-> Say we want to assign replica 3 then we have to ensure that the primary and
the secondary replica are already assigned and from that determine a plan.
So to do that we may have to enable the cost functions or we should add some
new methods to make LB in roundrobin to be aware of replicas.
-> Next is that the way we do in the current patch attached here actually
solved the issue because for the balancer it got all the regions (incluidng
replicas) and just applied the round robin part on it.
Will be back here.
> 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,
> 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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