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https://issues.apache.org/jira/browse/HBASE-18946?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16198278#comment-16198278
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ramkrishna.s.vasudevan commented on HBASE-18946:
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I now got the real issue why this happens. Need to check in other branches
which is not PRocV2.
Suppose we create a table with 20 regions and say replica as 3. Now we create
60 Assign procedures. Now all these assign procedures are added to a queue
'pendingAssignQueue' in AM.
There is a thread that executes the assignment of the regions in this queue.
So when ever all the 60 regions are added to this queue and the assignment
thread assigns them we have no problem. The Stochastic LB uses the replica
concept to ensure the regions are assigned properly. The Cluster and Cost
functions created per 'roundRobinAssignment' ensures that happens.
But when the multi threaded model executes differently like the 60 regions are
executed with 45 and 15 regions each then we end up in this issue every time.
Because the roundRobinAssignment Cluster creation is not global and it is per
assignment.
> 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: 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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